Version 4e PDF - Sherline Products

Version 4e (Linux v4.51), updated 5/5/08
Operating Instructions for the Sherline
Vertical Milling Machine CNC System
P/N 8540/8541, 8020/8021, 8600/8601, 8620/8621
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PRECAUTIONS
Do not connect or disconnect stepper motors when the driver box is
powered up. Always turn off power to the driver box before plugging
unplugging a stepper motor. Improperly connecting or disconnecting a
motor can damage it.
Before turning on the computer and booting up EMC, make sure the
power switch for the stepper motors on the side of the computer (or on
the 8760 driver box) is in the “OFF” position. After EMC is fully loaded
it is then OK to turn on power to the stepper motors.
Do not turn power on to the stepper motors unless EMC is already
running. Controls within EMC prevent overloading of the power supply
when multiple motors are powered up at the same time, but without this
safeguard motors or drivers can be damaged.
If operating the system outside the USA, make sure the 115/230 Volt
power switches on the computer and driver power supply are in the
correct position before turning on. The spindle motor will automatically
adapt to any current from 100 to 240 VAC, so no transformer or
switching is needed.
Finding the most current instructions
The most up-to-date version of these instructions can always be found on the Sherline
web site at www.sherline.com/CNCinstructions.htm. These instructions refer to systems
with the Debian version of Linux 4.xx distributed by Sherline starting January 1, 2005.
Instructions using the older 2.xx Redhat version of Linux will remain posted on the web
as well. (Typographical errors found in some of the sample g-code programs in the
instructions have been corrected in both versions.)
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CNC for Lathe Users
Purchasers of Sherline CNC lathe systems can also use these instructions, as the basics of
CNC apply regardless of the machine being run. Keep in mind that lathe operations will
require somewhat different g-code simply because of the way parts are made on a lathe.
Use of Non-Sherline Programs
Sherline cannot be responsible for the support of software or hardware products not
designed or sold by Sherline. For questions on Windows® CAD, CAD/CAM, control or
utility programs, please contact the seller of the software. It would be impossible
for Sherline to guarantee that g-code generated by any particular CAD/CAM program
will run on EMC without modification. A thorough knowledge of g-code programming
will always be useful to eliminate problems caused by post processors.
Safety Rules for Power Tools
1. Know your power tool—Read the owner’s manual carefully. Learn its application and
limitations as well as the specific potential hazards peculiar to this tool.
2. Ground all tools—If a tool is equipped with a three-prong plug, it should be plugged
into a three-hole receptacle. If an adapter is used to accommodate a two-prong receptacle,
the adapter wire must be attached to a KNOWN GROUND. Never remove the third
prong.
3. Keep guards in place—and in working order.
4. Remove adjusting keys and wrenches—Form a habit of checking to see that keys
and adjusting wrenches are removed from the tool before turning on any machine.
5. Keep work area clear—Cluttered areas and benches invite accidents.
6. Avoid a dangerous work environment—Do not use power tools in damp or wet
locations. Keep your work area well illuminated.
7. Keep children away—All visitors should be kept a safe distance from the work area.
8. Make your workshop “kid-proof” —with padlocks, master switches or by removing
starter keys.
9. Do not force a tool—Do not force a tool or attachment to do a job for which it was not
designed. Use the proper tool for the job.
10. Wear proper apparel—Avoid loose clothing, neckties, gloves or jewelry that could
become caught in moving parts. Wear protective headgear to keep long hairstyles away
from moving parts.
11. Use safety glasses—Also use a face or dust mask if a cutting operation is dusty.
12. Secure the work—Use clamps or a vise to hold work when practicable. It is safer
than using your hand and frees both hands to operate the tool.
13. Do not overreach—Keep your proper footing and balance at all times.
14. Maintain tools in top condition—Keep tools sharp and clean for best and safest
performance. Follow instructions for lubrication and changing accessories.
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15. Disconnect tools—Unplug tools before servicing and when changing accessories
such as blades, bits or cutters.
16. Avoid accidental starting—Make sure the switch is “OFF” before plugging in a
power cord.
17. Use only recommended accessories—Consult the owner’s manual. Use of improper
accessories may be hazardous.
18. Turn the spindle by hand BEFORE switching on the motor—This ensures that
the workpiece or chuck jaws will not hit the lathe bed, saddle or crosslide, and also
ensures that they clear the cutting tool.
19. Check that all holding, locking and driving devices are tightened—At the same
time, be careful not to over tighten these adjustments. They should be just tight enough to
do the job. Overtightening may damage threads or warp parts, thereby reducing accuracy
and effectiveness.
20. Don’t use your lathe for grinding—The fine dust that results from the grinding
operation is extremely hard on bearings and other moving parts of your tool. For the same
reason, if the lathe or any other precision tool is kept near an operating grinder, it should
be kept covered when not in use.
21. Don’t let long, thin stock protrude from the back of the spindle—Long, thin stock
that is unsupported and turned at high RPM can suddenly bend and whip around.
22. Wear your safety glasses—Foresight is better than NO SIGHT! The operation of
any power tool can result in foreign objects being thrown into the eyes, which can result
in severe eye damage. Always wear safety glasses or eye shields before commencing
power tool operation. We recommend a Wide Vision Safety Mask for use over spectacles
or standard safety glasses.
23. Disconnect the computer from all power sources before opening case—With the
computer power switch off, some of the internal components of your computer are still
electrical hazards and can provide a severe electrical shock. Disconnect the computer
from the power source before opening the case to eliminate this possibility of an
electrical shock.
24. Static electricity can damage your computer—Be sure you are properly grounded
before touching any components inside your computer. A spark of static electricity can
damage delicate circuits in some components in your computer. Either wear an approved
static electricity grounding strap around your wrist or touch the case of the computer with
one hand before touching any components with your other hand.
25. Be sure you know what will happen BEFORE pushing the [START] button—
Run your program in [BACKPLOT] mode before running the actual part to make sure it
will run the path your are expecting. Make sure your machine is in the proper home
position before starting the operation.
Electrical Connections
The power cord supplied is equipped with a 3-prong grounding plug that should be
connected only to a properly grounded receptacle for your safety. Should an electrical
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failure occur in the motor, the grounded plug and receptacle will protect the user from
electrical shock. If a properly grounded receptacle is not available, use a grounding
adapter to adapt the 3-prong plug to a properly grounded receptacle by attaching the
grounding lead from the adapter to the receptacle cover screw.
NOTE: The electrical circuit designed into the speed control of your lathe or mill reads
incoming current from 100 to 240 volts AC and 50 or 60 Hz and automatically adapts to
supply the correct 90 volts DC to the motor. As long as you have a properly wired,
grounded connector cord for your source, the machine will operate anywhere in the world
without a transformer. This has been true for all Sherline machines built since 1994.
STEPPER MOTOR CORDS: Do not disconnect the cable at the stepper motor end unless
absolutely necessary. It is designed for limited use and can be easily damaged. When
connecting and disconnecting the motors, always use the round plugs that connect to the
driver box cables. Do not pull on the wires to disconnect connectors—Grip the plugs
themselves.
CAUTION—Manual Adjustments Using the Handwheels
MANUAL MODE: A DC motor acts like a generator when cranked by hand. When
using the machine in full manual mode it is good practice to physically disconnect the
stepper motors from the driver board cables to prevent the generated voltage from
damaging components on the board. Cover the ends of the motor connectors with
masking tape to protect them from debris.
CNC MODE: When operating in CNC mode you do not need to disconnect the
handwheels when cranking slowly and over short distances to manually position the
slides. The motors are locked up when power is on so the power switch to the drivers
must be in the OFF position. For longer positioning travels it is easier to use the Jog
Mode and move to approximate position electronically. Final adjustment can then be
made with the handwheels (with power turned OFF). Do not turn the handwheels
manually faster than 1 rotation per second.
Lubrication
CNC machines require more attention to keeping the leadscrews properly “oiled” than
manual machines. When you crank the handles by hand you can quickly realize that a
slide is going dry because you can sense the results of the extra drag. A CNC machine
will not complain and will always work with the instructions that you gave it. You tell it
to run, and it will die trying to please you. The Y- and Z-axis screws can be easily oiled;
however, the X-axis screw needs special attention. You can’t see it because it is located
under the mill table. The best way I have found to lubricate it is to move the mill table all
the way to the right, put some oil on your fingertips and transfer it to the leadscrew. As
the table is moved back to the left, oil will find its way to the internal brass nuts.
Remember, that any type oil is far better than none. The slides also require constant
oiling. I believe these oiling procedures should be done after every four hours of
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operation. For more on lubrication see page 5 of the Sherline Miniature Machine Tools
Assembly and Instruction Guide that came with your mill.
CNC System Warranty
If within one year from the date of purchase of a new Sherline CNC system any tool or
component fails due to a defect in material or workmanship, Sherline will repair or
replace it free of charge. In addition, it has always been our policy to replace at no cost all
parts, regardless of age, which are determined to have been incorrectly manufactured or
assembled and have failed due to this cause rather than because of improper use or
excessive wear caused by continuous use in a production environment. In cases such as
this, Sherline will inspect the machine or part and will be the sole judge of the merit of
the claim.
Freight charges for returning a machine are not covered. Save the original packaging
material to use if the machine or computer must be returned to the factory for
service. Sherline will not participate in insurance claims where the sender didn’t make an
honest effort to package the items to prevent damage caused by normal shipping stresses
or repair said damage without charging the sender.
Merchandise that has been abused, misused, improperly maintained or insufficiently
lubricated is not subject to warranty protection. Proof of date of purchase and dealer
name may be required for service under this warranty.
Specific exclusion for wear due to production use
Although many Sherline tools have found there way into production environments, they
have been designed for intermittent use in home shops. It would be unreasonable to
expect a Sherline machine to stand up to the rigors of continuous production use.
Continuous use of stepper motor driven leadscrews in a production environment can
introduce wear that would be impossible to produce manually. Therefore, slides, gibs,
leadscrews, leadscrew nuts and bearings that are subject to high wear due to continuous
usage are not covered under this one-year warranty.
Non-warranty service and machine tune-ups
Sherline machines are easy to service, and all replacement parts are available from the
factory. However, if in the future you wish to return your machine for any reason to have
Sherline repair or adjust it, we will be glad to do so. Our shop rates are very reasonable
and our production people have all the proper tools and fixtures to repair or service your
machine quickly and return it to factory new condition.
Returning machines or parts for warranty or non-warranty repair
Before returning any tools or parts for repair, please call first and obtain a Return
Material Authorization (RMA) number so that we can process your order immediately
upon receipt. Remove all non-essential parts from the machine to save shipping weight
and return only the portion to be repaired. Wrap and package all parts securely so they
cannot move around in shipment. We recommend that heavy parts be double-boxed.
Include a brief written description of the desired repair and your return address and phone
number or e-mail address inside the box so we can contact you if questions arise. Repairs
are normally return-shipped the next workday after they are received.
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Technical Support
If you have a physical or electrical problem with a machine, component or accessory
manufactured by Sherline, please feel free to contact us at 1-800-541-0735, 1-760-7275857 or sherline@sherline.com. If you have technical questions regarding the
functions Linux or EMC that are not answered in these instructions, the Linux group
maintains an excellent web site at www.linux.org that has a search function and a lot of
helpful information. Remember that Sherline hasn’t charged you a single penny for the
Sherline version of the EMC program even though we have spent a considerable amount
of money and time adapting the EMC program to the Sherline mill. Our CNC instructions
also include a free basic course in the use of G-code, and the printed instruction manual
that comes free with each machine is the most complete of its kind. Beyond that, we
recognize that many of our customers are new to machining and to CNC, and we will do
our best to put callers on the right track to the information they need to get their new
CNC system up and running. Learning to use G-code and learning to cut metal beyond
what we provide in our instruction manuals must ultimately be the responsibility of the
machinist, but we will help where we can.
A short history of CNC
I’ve been personally involved with CNC since the early seventies and soon realized that
this was the way to make things. Back then all sorts of ideas were being tried to simplify
the mass production of machined parts. Many manufacturers were using hydraulic power
and came up with some interesting systems. The method of choice before NC (back then
they were called Numerical Control (NC) because the storage device was a one inch wide
paper tape) was a tracing system that duplicated parts by tracing them with a hydraulic
system controlled by a really neat valve controlled by a stylus that the operator would
move like a probe and the machine would duplicate their movements. Gigantic machines
were built around this idea for the aircraft industry.
Hydraulic CNC systems?
It was only natural that this was the group of manufacturers would be the first to try this
new field, and did they ever come up with some weird systems. You also have to realize
that electronics were also pretty crude during that same time period. My first NC machine
was a Cinematic manufactured by Cincinnati machine tool. It had ball lead screws driven
by hydraulic motors and was fairly reliable and quite popular at the time. Tool changers
were still in their infancy. I ran it until it was so out-dated that I gave it away when it still
ran. Another interesting point is this machine had a “wire wrapped” control with few
circuit boards. If a recent graduate of electronic engineering had ever looked into the
control enclosure, I’m sure his first comment would be “impossible.”
I thought I bought a telephone company
My first machine that was controlled by electronics turned out to be a disaster. I bought it
used and it had a stack of manuals 18 inches high. I never dreamed I was going to look at
every page but I did. When I opened the control and looked in there, I thought I bought a
telephone company. I believe there were 120 individual circuit boards and thousands of
individual transistors. It was manufactured by Edlund. We used to call it a “Deadlund.” I
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wasted more time and money on that machine than I care to admit, and I felt relived as it
was loaded on a truck for its final journey to the junkyard.
Problems with no memory storage
The way this machine stored memory was interesting. At this time there weren’t any
memory storage devices invented for commercial use. What this control did was feed a
single block of code (a block of code contained the instructions the machine needed to
make a single move) into a very long piece of Ni-chrome wire. The high resistance of the
wire would delay the signal long enough so the signal could be amplified at the other end
and sent back on the same wire without interference. The signal would then bounce back
and fourth until the machine had moved to a location that corresponded to that block of
code.
Sometimes I can be persistently stupid
New machines were thousands of dollars more than I could afford and not that reliable
either. I remember a friend who had a three-year-old machine that cost over $100,000
that needed service. The first thing the technician said was, “I didn’t think they had any
of these old bastards still running.” You can imagine how my friend felt when he made
that $2500 payment each month.
You’d think I would have learned by then, but I can be persistently stupid at times. My
next disaster was a MOOG milling machine. It used a Bridgeport base and didn’t have
leadscrews. It was entirely controlled by hydraulics. Movement was controlled by thin
plates that moved with the machine slides with accurate holes located at every inch. Pins
about 0.187" (5mm) would engage the proper hole and then another plate with holes
spaced at 0.200" would come into play, and the last 0.200" relied on a single turn of a
lead screw. The machine finally arrived at a position within a 0.001" of accuracy. I didn’t
realize it when I bought it, but I was horrified to find that this mother worked like a
player piano. The one-inch wide paper tape wasn’t read with switching devices like other
machines. It actually was more like a valve that allowed or prevented air to get to
cylinders that controlled hydraulic valves. When it read a block of tape (around 10 lines
of holes of 8 holes each) the SOB sounded like a steam engine. I chalked that one off to
having more balls than brains; however, we actually made more parts with it than we did
with the Deadlund.
It should also be noted that I’m sure that these early NC machines were the best that
could be designed with what was available, and the solutions that they came up with were
quite ingenious at the time. I’m looking back at it from a slightly humorous position and
in no way infer that the designers of that era weren’t up to the task. They just didn’t have
the tools to work with that we do today.
The course is set
At this time, NC machines could only cut straight paths, and as soon as the electronics
were available to store just a small amount of memory the new rage became “look-ahead”
control systems. This meant the cutting tools wouldn’t create machining problems when
they hesitated as the next block of information was read. Stepper motors were used for a
short period to drive the lead screws; however, within a few short years the entire
industry switched to DC motors. Encoders or resolvers were used to keep track of
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position. The DC motors controlled by fast computers and working in unison with
accurate ball lead screws created a system that was very close to where we are today;
however, they were slower and very expensive. Today, servo drives use AC motors
controlled by varying the frequency to the windings, eliminating the brushes needed with
DC motors. The latest innovation is linear motors that can move machine slides at
incredible speeds.
A new way of thinking
The marvelous part of the CNC revolution wasn’t just the fact that it was eliminating
workers from sometimes very strenuous and boring jobs; it was that there was finally a
method of cranking these handles in unison to do things that the best machinist in the
world couldn’t accomplish. By moving screws on the X- and Y-axes in unison, you could
machine tapers, circles and, in fact, any shape you wanted. This allowed engineers to
design parts with the shapes that they wanted, not just shapes that were possible to
machine using the old methods. Machines that cost thousands of dollars suddenly became
scrap iron. These new CNC machines didn’t care if they were cutting a complex shape or
a straight line. Whether the tolerance was tight or not the machine was always “right on,”
and the tools determined the tolerances.
Ball lead screws—the missing ingredient
The lead screws used on these machines should be mentioned. They are the interface
between the computers and the mechanics. The problem of backlash was solved with
“ball lead screws.” These screws have re-circulating balls that roll in a groove ground
into a shaft at a pitch of two tenths of an inch. The pitch on these screws has increased
over the years to achieve speeds over 1000 inches (25 meters) per minute. At a pitch of
.200″ (5mm), a lead screw would have to turn at 5000 RPM to accomplish this speed,
which is why ball lead screws have as high as one inch in pitch. Even more amazing was
the fact that they improved the accuracy as they increased the pitch. You can make a
.0001″ (.0025mm) correction on a good CNC lathe. Think about that. A slide will
accelerate to a speed of over 1000 inches a minute in less than a second, move a short
distance and decelerate, stop and still be accurate to one ten thousandth of an inch. The
ball screws must be very precise, because a lead screw would be useless if it had any
backlash (the amount you have to rotate a lead screw before the slide moves).
Ball lead screws are very difficult to make, which makes them quite expensive—several
thousand dollars for each axis. The people who solved the lead screw problem should be
commended as much as the electronic geniuses who came up with the computer controls.
At Sherline, we have CNC machines that have been running over ten years and still don’t
have any noticeable backlash.
Carbide insert tooling changed the entire machine tool industry
At the same time, carbide insert tooling became available and took the market over like a
storm. I don’t think I could have ever convinced a machinist in the fifties that some day
he would be taking 0.300" cuts on cold rolled steel at a cutting speed around 400 to 600
fpm (200 meters/min) using a 40 hp lathe at 0.020" (.5mm) feed rate for each revolution
with little carbide tools made using powdered metal technology and held in place with
little screws and still be able to get marvelous finishes on gummy old cold rolled at the
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same time. They do, and we at Sherline do all these things that give our customers a lot of
bang for the buck. The consumers of products that manufacture using this technology
benefit as much as the manufactures that use them.
Because lathes could also produce these types of moves, the large and expensive form
tools were on there way out. This may not seem significant, but by generating rather than
forming shapes, these shapes could be far more precise, and at the same time machines
didn’t have to be so massive to prevent tools from chattering. Hand scraped ways were
replaced by frictionless, ingenious slides that lasted for years with little maintenance.
Because there is always the possibility of a crash, machines are no longer built where the
headstock is an integral part of the base casting, and in most cases they can be realigned
if one of these disastrous events should happen.
Why I love CNC robots
In closing this section, I firmly believe that these machines that we call CNC are the
robots of the future and I truly love them. They have allowed me, Joe Martin the
designer, to design the parts that I’ve always wanted to design without dumping my
problems on Joe Martin the machinist, who must produce parts for Joe Martin the
businessman, who can supply you, the customer, a fairly priced quality product and at the
same time allow Joe Martin the owner a reasonable profit to buy more of these marvelous
CNC machines, of course. And so it goes.
Even though this doesn’t do the subject justice I thought you might find that interesting.
It’s always wise to see at least a brief history of a subject before becoming part of it, even
if it’s only statistical.
Here is something I wrote in my book that’s available online that you may find
interesting. See http://sherline.com/business.htm.
“THE NEW MANAGERS
CNC machines allow a smart worker to produce more work than ever. Rather than
eliminating the need for intelligent workers, these machines require organizational
skills that few managers have. The machines they control are very complex, and
the employees who can control these machines are equally as valuable to a
company as that of standard managers. In the past managers were considered
people managers. The managers who control these machines are robot managers.
When you consider how important these machines have become to the quality and
efficiency of manufacturing a product, the group of workers that controls these
machines will soon be equal to the managing staff of any company in prestige and
wages. Today’s management still hasn’t grasped this concept, but soon they will
be forced to accept this condition when they find their million dollar machines
operating at half speed.”
This CNC class is open to those willing to work hard
In order to make the following instructions more interesting for me to write and you to
read I’m approaching the teaching of CNC programming the same as I would as if I were
teaching a small class of students. The students who attend these specialized classes later
in life have various reasons and expectations for being there, and I’m trying to address
the whole class as I write. When I take off on a tangent I’m addressing individual
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students with a different background who I visualize sitting in the class and answering a
question that I believe may be asked in a similar class, so please bear with me. I don’t
want any of my students left behind.
Enjoy the flight
In many of the coming examples I also describe the movement of the spindle as an
aircraft that you’re riding in. This may seem “far out there,” but CNC milling is a 3D
world, and if you try to describe these movements in the movement of the table slides
you’ll soon not know whether you are coming or going. You have to visualize the work
staying still while the cutter moves. Again, bear with me and enjoy the flight.
A different way of learning
Long ago I became aware of the success rate of people who, when left alone with their
video recorder and an instruction manual, failed to pass the test and had to stay up late to
turn on their recorder to record a show they wanted to save. From their own statistics you
would think manufacturers would have attempted to teach in a different manner, but they
don’t. The products get more complex, making the instructions more complex, and the
poor consumers of these products are at a loss. I don’t teach using these methods because
they obviously don’t work. With my instruction you won’t be sure if you’re reading a
novel or an instruction manual, but I’m sure you’ll be able to program and make a part
when you get to the end.
The first instructions I completely wrote for my tools (I had written instructions about
radio control equipment and rules for RC events in the past) were how to cut a screw
thread using a rather crude device I designed (but which works well) for a Sherline lathe.
I was surprised how few calls on how to use it came in after I sold my first 200, because
it is a bit of a complicated thing to do. I then started to wonder if anyone was using it, and
you’ll never know how relieved I was when a customer came in with a bunch of parts
that he made with threads on them.
I knew I was on to something and have always written in this style ever since because it
works. It had to work because at that time I was the only one at my company who could
answer questions of this type, and I didn’t have the time. The fact that I’m a self taught
person probably has something to do with it. I even went on to write a couple of books in
this style that were well received.
A new challenge
I remember getting a call from Sears about my folksy style of writing that didn’t follow
Sears’ instruction guidelines about the screw cutting attachment. I asked him how many
calls they had received about how to cut threads using it. He answered, “None.” I asked
him who there could answer a technical question of this type. He answered, “Nobody.” I
said, “With this being the case, don’t you think you should leave well enough alone?” I
never heard from him again. Right now, I’m looking at these instructions as one of the
biggest challenges I’ve ever taken on as an author, and I don’t plan to fail. The average
instruction manual written on this subject is two to three hundred pages of very technical
reading. You’ll never crack a smile reading one of these manuals. I’ll do it in less than
fifty.
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The only students I hired who learned CNC had good teachers, not good training
manuals. In fact, I can’t think of any employee in the last 30 years that I’ve ever hired
who learned CNC programming and how to run these complex machines on his own.
You will! I had to learn on my own because I was so broke after I bought my first NC I
was out of choices. I learned by staying up late, working my ass off and making costly
mistakes. I would have given my left you-know-what if I had something like this to read
rather than reading the junk written by professors trying to prove how smart they were to
other professors rather than attempting to teach their own students.
Sherline customers want to build components
I saw the customer who was going to read these instructions as a person who wasn't
particularly interested in computers or gadgets and was only interested in making parts. I
believed they were curious about CNC and wanted to learn about it without spending too
much money. They probably haven't tried to learn how to do something this complicated
in the last 20 years. Remember that CNC is a new way of doing and thinking about the
machining process, and I believe I’ll help get your brain in tune with what you are about
to learn with my ramblings.
Learning while you work
A student of this class could be already working at the trade. Words of advice for this
group: You can’t afford to have idle thoughts as you load parts on machines that other
people set up and wrote the programs for unless you are satisfied to load parts for the rest
of your life.
First study the mechanical part of the setup; things like how the part is held and the type
of cutting tools used and how long they last. You have to show some initiative and start
analyzing the program you are running and ask intelligent questions. Notice, I said
intelligent questions. Bosses are usually smarter than you think they are, and they easily
know when some when clown is pulling their chain. Don’t ever make suggestions unless
you are sure you are right. A better way to make a suggestion of this type is to ask them
just why the job is set up or run the way it is rather than your way. That way you’re not
threatening them with your question, and they’ll appreciate a chance to teach you if you
are wrong. If you find out you were wrong, it gives you a way out by saying that you
were sure that they must have had a good reason. It wouldn’t hurt to let that rule work its
way into your personal life.
When you start studying their programs, you’ll find them written like a story. Just like a
book, the better the author, the easier the program is to read. Each tool used will have its
own chapter. (In the real world of machining you’ll run few machines without automatic
tool changers.) Study these chapters one at a time and watch what the machine does as
the program advances. In case you didn’t realize it, I’m also instructing all you hobbyist
out there on how to organize your programs and setups. Plan them like someone else is
going to run the job and pick apart your own work. If you don’t, you might find yourself
trying to machine your vise off the table.
Getting you into the learning mode
I also felt that people of this type would want to read something about what they are in
store for before they started. I wanted my customers to understand just how difficult CNC
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programming can be to learn at the start and just how interesting it can be at the same
time. In other words, I felt “Joe home machinist” doesn't stand a chance unless he's
inspired to do so, and in my own way I’m trying right now to inspire you to learn how to
program and use these marvelous new CNC machines. I know how easy it is for you to
go back to the way you already know or forget the whole idea. I don't want customers
who think it'll be easy to learn because they'll be unsatisfied from the beginning and take
out their anger on Sherline.
You’re about to learn how to control your robot
These aren't instruction about operating a simple single system like a VCR, but
instructions about controlling a very complicated device. You are not operators of these
marvelous machines; you are masters telling your robot what to do, and you, the
controller, have unlimited choices to make. I want to get this concept through to that
average customer I mentioned, yet I know that only one out of five professional
machinists I know seems to really understand this point.
I’m going to be a student in my own class
I was shocked at just how much I had forgotten about the process of CNC programming.
I probably know as much as anybody of what you can do with CNC machines, because I
own at least twenty modern machining centers, yet I haven’t really written any code in
fifteen years. After thinking about it for a couple of days while unsuccessfully attempting
to write a simple program I decided this is a good thing. I also decided that I’d learn this
from the Linux site on my own and not use the books that were available to me. I
believed that if I wrote the instructions as I learned how to program EMC myself I’d
write better instructions; after all, all you have to be is one page ahead of your students to
teach. Just joking, teachers.
Something for nothing
Sherline Products Inc. is not charging you for this EMC program, and it is free because of
work done by NIST (National Institute of Science and Technology), a government
funded organization. The EMC (Enhanced Machine Controller) was written by the NIST
and is a very sophisticated program. We all now have the benefit of millions of dollars of
programming along with the source code, if needed, simply by asking.
We all owe thanks to the EMC group
At the time this program was written it was thought that only very advanced
programmers and scientists would be using a program such as this, and the average
person stood little chance of making it functional. Fortunately for us, a lot of very smart
people before us, donating their time, started developing a programming interface that
allowed both businesses and hobbyists to take advantage of what they had done without
being engineers. I’m very pleased with what they have done. This group still works
together through the Internet, and help is available through Internet chat groups. Many
people have donated much of their time to make this system “user friendly.”
The EMC program operates under the Linux operating system, which is also a free
system, and it would be wise to operate it from a dedicated computer for this task. A dual
boot system can lead to problems, because Microsoft code has been purposely written to
12
be the dominant control of your computer whether you want it or not. I like the Linux
concept of people working together where all have the benefit of any single person’s
work. For example, these instructions will have a Sherline link placed on the EMC for all
to read whether they are Sherline customers or not. It will be my donation towards a
successful system available to all. I’m learning how to program EMC by using the
internet site put together by dedicated EMC users, so you can also fall back to their site
for help. http://www.linuxCNC.org/
This is going to be easy if you do it my way
The Linux operating system is similar to use to all others, and I’ll try and mention things
that are a little different in using the EMC program. To start with, you don’t have to
double click to enter a program, so a single click on the big red “S” (Sherline, not
Superman) with the file name “inch_freq” underneath, and after a few seconds you’ll get
the graphical interface to the EMC. Well, that was easy. Now, after BS-ing you to death
on how hard this was to do I’m going to show you how easy this can be, but only if you
do it my way.
Computers have the patience of a saint
If you’ve had little computer experience the first thing you will learn is that computers
have the patience of a saint. If computers were more human they would probably like to
toss their operators out the window as much as frustrated operators want to do the same
to them. The only way you can keep a computer from giving you an error message is to
not give it errors. The tricky part is computers don’t always tell you the error to fix or
how to fix it. Computers just tell you that there is an error of a certain type. This can
become maddening, and you have to know when to take a break and walk away. Things
of this nature are the worst when, for the sake of your own sanity, they should be the best.
In many ways, learning programming is similar to learning machining. You can’t take
short cuts. If you find yourself going in the wrong direction, back up immediately.
Learn machining first
If you know little about machining and little about computers I’d suggest you first
concentrate on learning about machining. How can you expect a machine tool and a
computer to carry out your commands if you don’t know the commands to give? Above
all, don’t start with a project so complex you don’t stand a chance in hell of succeeding.
Let each simple problem solved have its own rewards in knowing you just traveled
another block further down the CNC machining super highway, route EMC.
NOTE: I have written a book called Tabletop Machining that is an introduction to
metalworking at the small end of the size scale. Details can be found at
www.sherline.com/bookplug.htm. If you are new to machining, you will find the
information in this book quite helpful.
You will be learning the CNC language of the robot world
The standard “G” code method of programming is to simply replace the manual inputs
into a machine (cranking the handles) with the commands that have become industry
standards. This is the method you should learn before learning any other method of
programming. It is the basic way that CNC machines “talk” to other CNC machines.
Even if a simpler system were available today I still wouldn’t teach it. It would be similar
13
to teaching a language that few citizens of the world spoke. Programs written using gcodes can be read throughout the world. g-code standards came about very early in the
game because this game was controlled by engineers rather that marketing people.
Contouring programs—another world
Programs that allow you to do contouring quickly become very complex. Today there are
some affordable programs available for sophisticated hobbyists. These programs can
create as many problems as they solve, because of the complexity of each program. Each
program has to work with other programs, and each program has its own set of complex
rules. If you think you can learn these programs easier than you can solve a couple of trig
problems you’re in store for a rude awakening; however, if you already know how to use
3D CAD programs you could quickly find these programs very useful. It should also be
stated that it is the only way available to create contoured machined shapes.
What it costs in the industrial world
The basic method that these programs work together in the industrial world and the cost
of these programs is: 1) The part is designed using a modeling program ($5000 to
$10,000), 2) The modeling program is converted to a CNC program (another $5000 to
$6,000) and 3) the resulting code is run on a CNC machine starting at ($25,000) that
makes the part. The people who can operate these systems are carefully chosen, trained
and well paid. The fact is that any business has no choice except to use the program they
purchased, because the programs cost so much and are so very necessary to remain
competitive in today’s world. They have to spend a great deal of money to accomplish
this, while the hobbyist has a choice.
Today’s low-cost programs were once complex, expensive programs
The business world understands how complex it is to implement these procedures; the
hobbyist doesn’t. Because the hobbyist may be purchasing a program that cost thousands
of dollars just a few short years ago for a few hundred dollars, the programs themselves
haven’t become less complicated. They only cost less! In your mind you may be having
visions of complex shapes being machined with little effort on your part while your two
thousand-dollar investment turns out parts that the old masters of the machine trades
would envy. Well my friend it’s possible, but it’s time to come down to earth and again
think about the complexities of doing so.
Cutter compensation—what makes CNC work in a machining environment
I could have sneaked out the back door and only wrote instructions for a couple of simple
moves without cutter compensation and let it go at that; but deep down inside, I’d have
known I was cheating you out of the real benefits of CNC. I believed that if I started
teaching you to use this marvelous programming tool right at the very start it will soon be
second nature, and our class will leap-frog ahead of our competition with those thick
boring books being taught by instructors I wouldn’t let near the least expensive CNC
machine in my shop.
If you take the effort to learn this method of programming at the start along with a little
simple trig, you’ll find it well worth the effort. Cutter offsets are the way you control size
with modern CNC machines. When you start making more complex parts and you don’t
use cutter comp you’ll have to change the basic numbers of your programs to make a part
14
on size. Sounds simple enough until you find that every time you correct a number here
you end up screwing up another number there. Take my thirty-five years of experience in
dealing with CNC and accept this cutter offset stuff as a fact.
I can’t help anyone who isn’t willing to work hard
Back in ancient times the great mathematician Euclid told a Pharaoh who wanted to learn
geometry the easy way that Pharaohs had to walk down the same road as scholars to
education. In a sense I’m also stating to you that you will have to learn programming the
same way as I’m about to, and at this time I’m only a couple of pages ahead of you. I am
certain that if I sat by the phone and answered questions twenty-four hours a day, and I
don’t plan to, I couldn’t help those who aren’t willing to put forth the effort it takes on
their own to learn to work with these marvelous tools.
Route EMC
This road that you are beginning to travel can become one of the most interesting roads
you have every traveled; however, you must take the time to gather the facts that can
make a trip so interesting. Instead of seeing great ancient cites on this road we’ll be
gaining the knowledge that will make our next stop even more interesting and more
complex. We’ll study a little and then apply these rules to your machine. We will first
make simple moves that become more and more complex and at the same time more
interesting as we travel on. Eventually we will reach Martinsville, a city on this road,
where you will have so many choices as to the direction to travel that you’ll be leaving
me and heading out on your own to design and build things that you never thought
possible in the past. The rules and facts that you will learn on this road will allow you to
have a machine at your control that home machinists a few short years ago couldn’t
dream of. Take the time to enjoy this trip because you’re on a road with no end if you
have set your goals correctly.
You may want to consider a CAD program in the future
I’m going to close this section off by inserting something I wrote about learning and
using AutoCad®. The ease with which many of the programming problems can be solved
has to be mentioned at this time; however, I wouldn’t recommend dropping what you are
doing. From what I understand there are several excellent programs available at very
reasonable cost, but I don’t want to recommend any particular program.
The following paragraph is from my book Tabletop Machining. It covers some of my
comments about learning to use a CAD program.
“Learning AutoCAD®
The first task I took on to learn the program was to lay out and design a set of
bevel gears that could be cut on a Sherline mill using a rotary table mounted on an
angle plate. By drawing the cross sectional view accurately, the angles needed to
cut this gear could be taken directly off the drawing without using a trig table or a
calculator. I was beginning to see the light.
I’m getting pretty good at using the program now and it has put a lot of the fun
back in designing for me. Looking over my partner Carl’s shoulder at an assembly
designed by computer was of no help for me, and I would need a standard full
15
size or larger layout to design with. I’ve since found that doing the design totally
myself, it has become the perfect way for me to work. I love the program. It has
become the perfect program for a designer and manufacturer like myself and has
made me more productive than ever.
I’m fascinated with the program because it does a drawing without errors when
used properly. The program eliminates much of the boredom of adding and
subtracting numbers as you go. Accuracy isn’t attained by the precision of your
lines but rather by the accuracy of the information the program is given. Angles
are not derived from a protractor and using divider points but from calculations by
a computer to as many decimal places as needed.
I learned drafting in high school back in the fifty’s. My problem was I was a
“slob” when it came to drafting a pretty drawing. My numbers and views would
be correct, but my lettering and lines weren’t neat enough. Things have changed
now with the aid of this program and my lettering is just as good as the best. I can
no longer spill gobs of ink on an almost completed drawing and have to start over.
I can change my mind as much as I want without irritating anyone. I’m a happy
man.”
-------------------------------------
16
Operating Instructions
Part 1
Instructions: Mill vs. Lathe
These instructions were written primarily for using the CNC system with a mill. A CNCready Sherline lathe can also be controlled using the same computer and driver system.
You would simply plug the crosslide stepper motor to the X-axis cable and the leadscrew
stepper motor to the Y- or Z-axis cable. Writing a program for the lathe is a little different
in that you must remember that when you program a distance for the X-axis travel, the
part diameter will be reduced by twice that amount. This is because you are taking that
dimension off the radius of the part, which is one half of the diameter. Other than that, a
little logic on your part should be able to accommodate the differences between the
spinning cutting tool/moving part on a mill and a spinning part/moving cutting tool on a
lathe. Because of the extra mass of a spinning chuck and part, extra caution should be
taken to make sure your program is not going to cause any interference between crosslide
or toolpost and the spinning chuck/part once it is running.
System Components and Connections
17
System components:
1) 1-5/8" manual handwheel
2) Z-axis stepper motor
3) Stepper motor mount
4) Sherline vertical mill with drill chuck, headstock spacer block, hex adjustment keys
and spindle bar
5) Backup Linux/EMC installation CD, Sherline instructions CD and Vector32 CAD
program CD
6) Y-axis stepper motor
7) X-axis stepper motor
8) Cable for optional A-axis connection
9) Computer with CD-ROM and Floppy drives, keyboard and mouse
10) On/Off switch for stepper motor power supply
Connections on back of your computer:
1) Keyboard connector cable (purple)
2) Mouse connector cable (green)
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3) Computer power switch
4) Connector from driver board to parallel printer port
5) Power cord
6) Connect your monitor here (blue)
7) On/Off switch for driver power supply
8) Output cables to stepper motors for A-, Z-, Y- and X-axes
9) Stepper motor driver power on indicator light
NOTE: The 115V/230V selection switch is located under #3 above. The separate voltage
selection switch for the stepper motor power supply is located inside the left side of the
case on the side of the power supply near the bottom of the case.
Assembling your system
Getting your system up and running is a simple task. It consists of assembling your mill
and connecting it to the computer as follows:
Mill
Unpack and assemble your machine according to the instructions included in the Sherline
Assembly and Instruction Guide packed with the mill.
Computer connections and starting up
Unpack the computer and enclosed components. Connect the stepper motor cables
leading from the back of the computer to each of the three stepper motors. A fourth cable
is unused unless you have purchased an optional rotary table that can be connected here
as a 4th (A) axis. Plug the purple keyboard cable (Ref. #1 in the previous photo) and the
green mouse cable (2) into their receptacles. Plug your monitor to the blue monitor
receptacle (6). If not already connected, plug the free end of the 25-pin parallel cable in to
the printer port (4). Insert the female end of the power cord into its receptacle (5) in the
computer and plug the male end into a properly grounded wall socket or surge protected
power strip. Turn on the computer and monitor but leave the power switch to the stepper
motors in the “OFF” position for now. Wait until EMC starts up before turning on power
to the stepper motors with the toggle switch on the left side of the computer case.
NOTE: If you start EMC and run a program and the screen shows the program is running
but the stepper motors are not moving, make sure the Parallel cable is plugged in as noted
above.
Opening the instructions file on the computer
If you are not familiar with Linux, you will find the desktop that opens when your
computer starts up to be comfortingly similar to the Windows® or Mac® desktop you are
used to. On the desktop you will see icons for several files. Using your mouse, click on
the file labeled “Sherline EMC Instructions” to open it. The instructions can also be
found on the enclosed CD as well as at Sherline’s web site at
www.sherline.com/CNCinstructions.htm. Please read all the instructions before
attempting to use the EMC program to run your mill. CNC machining is a complicated
process, and you will be directed at the proper time to run a program on the machine once
you have gained the knowledge you need to do so.
19
EMC—Still the latest and greatest
I chose the EMC program to work with because: 1) EMC uses coding standards that are
used in the modern machine tool world, 2) You will not be dealing with an outdated
programming system, 3) EMC can deal with the cutter compensation (cutter comp) that is
needed to make complex parts in an efficient manner, 4) The cost saved by not having to
pay for this marvelous programming system will allow you to purchase a separate
dedicated computer to drive your mill and 5) There’s great bunch of smart people
working on EMC to constantly improve the system and make it easier to use in the future
and remain current.
Basic operation of the computer and file navigation
Booting up
Before turning on the computer, make sure the 115V/230V switches on the back of the
computer and on the side of the stepper motor power supply inside the computer are set
to the proper voltage for your local electrical current. (Default setting is 115 VAC.) Also,
make sure the ON/OFF switch for the stepper motor power supply on the left side of the
computer is in the “OFF” (down) position. Once the EMC program is fully up and
running, power to the stepper motors can be turned on. Also, do not turn power on to the
stepper motors unless EMC is already running. Controls within EMC prevent overloading
of the power supply when multiple motors are powered up at the same time, but without
this safeguard motors or drivers can be damaged.
Opening the EMC Program—Login and Password
When starting up, the computer will boot up without asking you to log in. If you log out
of the desktop and log back in and get a login screen, enter “sherline” for the login (in all
lower case letters) and “sherline” for the password.* After completing the login entries,
left click the [Go] button with your mouse, and the desktop will appear.
*NOTE: For earlier systems using BDI version 2.18 the login is the word “root” and the
password is left blank. On versions 4.05 and higher a Sherline account is also available,
so you should enter “sherline” instead of “root.”
To open EMC, click on the “Sherline CNC (inch)” or “Sherline CNC (metric)” icon on
your desktop. If they don’t appear there, move your cursor to the lower left corner of the
screen and click on the icon with the large “K” in it. Scroll through the menu to where it
says “EMC.” Choose either the inch or metric version of EMC and click on your choice.
This will open the proper version of EMC, and you are ready to get started. (You can
click on either icon and drag it to the desktop to create a shortcut for future use if one is
not there already.)
Instruction files
The instructions for the use of your system are preloaded on the computer. To find them,
click on the “S” logo on the desktop labeled “Sherline EMC Instructions” to open the
HTML version of the instructions. There is also a folder labeled “Instructions” that
contains the PDF and HTML versions in both full length and the shorter “print” versions.
The “print” version contains only the pages relating to learning g-code in case you want
to print it out and refer to a hard copy when working with the examples. The files are also
20
on the backup CD that came with your system. Included along with the PDF and HTML
versions is a MS Word (.doc) version should you wish to open it on a Windows®
machine that has Microsoft Word® installed. The most current version of the instructions
can always be found on the Internet at www.sherline.com/CNCinstructions.htm. PDF and
HTML files can be opened in Linux or Windows.
Shutting down the computer when done
To properly shut down your computer after you have closed EMC click on the “K” icon
in the lower left of the screen and choose the appropriate command from the menu that
pops up. (You can also right click on the screen to bring up this menu.) You can choose
to log off, restart or shut down.
Emergency stops
If you see a physical “crash” is about to occur, you can use the mouse and the [Feedhold]
command to stop the program, remove the obstacle and then use [Continue] to continue
with the program, but that can take too much time in a panic situation. The fastest way to
stop the stepper motors is to turn the power switch on the side of the computer to “off.”
The spindle will continue to run, and the machine will have to be re-homed and the
program restarted, but turning off power to the stepper motors while they are running will
not cause damage. Running a slide until it hits a hard stop should not cause any physical
damage either, but power to the motor should be turned off either by stopping the
program or turning the stepper motor power supply switch to OFF as soon as possible to
prevent possible overheating of the stalled motor.
A fast way to kill power to everything at once in an emergency is to plug all your power
cords into a single power strip that is mounted within easy reach near the machine.
Hitting the ON/OFF switch on the power strip kills power to the computer, spindle motor
and stepper motors all at the same time. The computer will have to be restarted and the
machine returned to the home position, but it will not damage the computer or EMC to
turn off power to it when EMC is running, and it might save a valuable part that is about
to be destroyed.
Transferring G-code files from another computer
1. On the computer you use to generate your G-code, save your G-code text file to a
floppy or CD in Plain Text (.txt) file format. Program files created in EMC will
automatically be saved with the .ngc extension. Either can be read by EMC.
2. Insert the floppy disk or CD containing your file into the appropriate drive on your
Sherline Linux computer.
3. On the desktop, click on the “CD” or “Floppy” icon of the drive where your source
disk is located to open a window showing the contents of that drive.
4. On the desktop, click on the “Home” icon and then open the folder called “gcode.”
5. Click/drag the new file from the floppy or CD window and drop it into the “gcode”
window.
21
The Desktop with two windows open for transferring files.
Above is the desktop with both the “gcode” folder window and the floppy drive window
open. Using the mouse, put the cursor on the file you wish to transfer. Click the left
mouse button and keep it held down and the file will be highlighted. (If you just click on
the file and release the button, the file will open.) While still holding the button down,
move the mouse to drag the icon of the file from one folder window to the other and then
release the mouse button. A dialog box will appear offering you a choice of moving or
copying the file to the new folder. Use the [Copy Here] command. A copy of the file will
now be added to the target folder and the original will remain in the source folder.
Saving a file created or modified in EMC to your “gcode” folder
1. On the top menu bar, make sure the “Editor” box is checked (filled with color).
2. If the editor window is not displayed as the main window, click on that window to
cycle through the checked functions until the window showing the lines of G-code is
displayed.
3. The main window will now have a small menu bar above it where you can select “File
> Save As.” When you do, a window will open.
4. The default directory to save programs should be the “g-code” folder. If it is not, in the
file saving window click on the file icon in the upper right corner of the window and
navigate to “Desktop > Home > Sherline > gcode” to select the gcode folder.
5. In the “Name” bar type in a file name and then click the [Save] button.
You can also save a file directly to a floppy disk rather than to the “gcode” folder by
navigating to the floppy drive instead of the “gcode” folder in step 4 above and then
naming and saving as in step 5. Remember to “Unmount” the floppy drive before
removing the floppy disk to complete the saving process. (To unmount the drive, right
click on the floppy drive icon on the desktop and select “Unmount” from the menu that
appears. Do not remove the floppy until the light on the drive goes out.)
22
Transferring a file from your “gcode” folder to a floppy
1. On the desktop, click on the “HOME” icon and then the “gcode” folder to open a
window showing the contents of the “gcode” folder.
2. On the desktop, click on the icon for your floppy drive. This mounts the drive and
opens a window showing the contents.
3. Click and drag the file to be saved from the “gcode” window to the floppy drive
window. When the mouse button is released a small menu will appear. Select “Copy
Here”. Finally, click the “X” in the upper right corner of the floppy drive window to close
it.
4. The floppy icon on the screen will have a small green arrow in the lower right corner.
This means the drive is mounted. To complete the saving process the drive must be
unmounted. Right click on the floppy icon and select “Unmount” from the menu. Do not
remove the floppy disk from the drive until the light on the drive goes out indicating the
copying process is completed.
NOTE: In this version of Linux you can name files whatever you want on your computer,
but they cannot be copied to a floppy disk if they have a file name longer than eight
characters.
What’s in the “gcode” folder?
When you open the folder called “gcode” there are already several programs we have
pre-loaded that you can run or modify. Here is what they are called and what they do:
0-new.ngc—A blank program ready for you to open and rename to create your
own programs
TheGreatRace.ngc—A triangular aircraft race course used as an example in the
instruction manual. Note: This is the only example given in the Sherline
instructions that you don’t have to type in yourself because it is lengthy for what
it does.
The following programs are written by the EMC group as examples of
different types of programming techniques and haven’t been fully tested by
Sherline. Ray Henry provided the explanations.
3D_Chips.ngc—This little penguin is the EMC mascot. It is written using metric
dimension but can be run on any mill. It is a bit too large to run directly on the
Sherline mill but is a great sample of contouring that will go quite a ways in foam.
3dtest.ngc—Runs X, Y and Z axes to draw circles in several planes (on-screen
use only, not for cutting an actual part). Run this from near the center of each axis
and it draws a circle and the letters of the plane on which the circle lies. This can
be handy when you change the angle of view of the plotter, because it will show if
you are looking through an axis because the lettering will be backwards or upside
down.
bbxy.ngc— (Metric) This program moves the cutter in about a four-inch circle in
one direction and then the other. There is an m00 between the direction change so
you need to press [Resume] or <s> on the keyboard
23
bbxz.ngc— bbxz.ngc is the same as bbxy above except that it makes
circles in other planes.
bbyz.ngc—bbyz.ngc is the same as bbxy and bbxz above except that it makes
circles in other planes.
cds.ngc—Circle Diamond Square (cds) is the original proof that the EMC
interpreter could run a milling machine. It is also a bit large for the Sherline mill
but works great in the backplot mode. It allows you to change views and look at
the various parts of a milled cube.
diag.ngc—Tests movement of each axis using small incremental moves. Hint—
You will want to rapid to 0,0,0 before you start this program or have something
else to do.
skeleton.ngc —A sample of code used to create a standard starting and ending
condition for a program. This does not show much if you run it but you can copy
and past it into your programs and then paste your code in the center. That way
you can be certain of the state of the machine after each run.
Dome_Test.ngc—Runs X, Y and Z axes to create a slight domed surface.
isd.ngc—As well as nist.ngc and nist2.ngc are variations of a router program that
cuts a NIST (National Institute of Standards and Technology) logo. There is an
error near the end of the code in one of them. See if you can find it. These take a
while to complete.
Opening the new file in EMC
1. Open EMC.
2. Click the [AUTO] tab along upper menu bar.
3. Click the [OPEN] tab on lower menu bar.
4. Highlight the file you want to open by clicking on it.
5. Click the [OPEN] box.
Installing a CD writer (CD-RW)
As of August, 2006, a CD-RW (Read/Write) drive is installed as standard equipment in
Sherline CNC computers in place of the earlier CD-ROM (Read Only Memory). For
those reinstalling Linux/EMC on their Sherline computer and for customers who are
using their own computer with a CD writer and installing Linux/EMC themselves, note
the following new instructions:
When you right click on CD-RW icon, unlike in previous versions where a CD-ROM
was used, the menu has changed. Instead of Eject it now says Actions, and after that
there are two options to choose from: Eject or Create Data CD with K3b.
Added to the K-menu is Multimedia > CD & DVD Burning (K3b). This application
allows you to burn CD’s (or DVD’s if you have a DVD writer installed.)
How to use K3b to write a g-code file to a CD
•
Click on the K-menu icon > select Multimedia > click CD & DVD Burning
(K3b)
•
Wait until the software starts and boots up.
24
•
From the Welcome menu, there are four options to choose from. Click on New
Data CD Projects and a new configuration screen will appear.
•
In the upper left corner from directories select Home > g-code. Next, click on any
file in the upper right corner.
•
Press [CTRL] + [A] to select all files or hold down [CTRL] and choose the files
you want to copy to a CD. Then, drag and drop all files to the space at the lower
right.
•
Files will be transferred and ready to burn in couple of seconds. (How long
depends on the size of the files.)
•
Insert a blank CD in the drive
• In the lower right corner click on the Burn button.
After burning is completed there is no need to save any files, so click Discard the
message after burning is finished.
The K3b program offers a number of additional options that you may explore on your
own.
Familiarizing yourself with the control panel
The Sherline Graphical Interface
By Ray Henry and Joe Martin
Start your engines
After having connected everything as shown in the reference photos above you will need
to turn on the computer but not the motor drivers (the drivers are the individual circuitry
that control the stepper motors) to see how this system runs. The power switch for the
computer is located on the front of the computer. The driver power switch is located on
the left side of the computer as indicated in the above photo. Up is on, and down is off.
When the computer is turned on, text will start scrolling on your monitor and the desktop
will appear. This will allow you to have access to various Linux programs; however, the
only program that Sherline will be using is the EMC metric or inch programs. Choose the
program that represents the leadscrews that are installed in your Sherline machine. Unlike
Windows, a single click on the appropriate icon will load EMC. A photo of the CNC
mill will appear and then the EMC program will open. Unlike earlier versions you will
not be asked for a login or password. (NOTE: If you log out and log back in you will be
asked for a login and password. In machines with EMC installed by Sherline the login
will be “sherline” and the password is also “sherline.” If you have done the installation on
your own machine, the login and password will be whatever you set up in the initial
installation, so do not forget what you chose.)
You can also find these programs by clicking on “K” icon in the lower left corner of the
screen, EMC > Sherline CNC (inch) or Sherline CNC (metric). This will initiate the start
of the Sherline EMC system which will take less than a minute.
I had Ray Henry put together the interface specifically for the Sherline CNC. He also
wrote much of “The Sherline Graphical Interface” section of the instructions. Many of
25
the features of the standard EMC program were removed for the Sherline interface
because they didn’t apply for a mill of this size and type to keep things as simple as
possible. Sherline machines do not have limit or home switches and do not have direct
control of spindle speeds and such. It is a general motion interface to the EMC. With it
you can jog any axis. You can set coordinate systems and tools. You can verify and view
the spindle path and motion in a built in program called “Backplot” and dry-run a
program before running the machine. The panel is laid out in a sensible manner and is
easy to understand.
FIGURE 1—The control panel screen
The screen is laid out in sections. The first row is the menu bar across the top. Here you
can configure the screen to display additional information. The small buttons that are
located left center of the command indicate that they control the large blank section of the
control panel that is sometimes called a “pop-in.” This will allow you to view the editor,
plotter, tool page and coordinate page. If more than one pop-in is active (button shown as
red) you can “toggle” between these pop-ins by right clicking anywhere within the pop-in
screen with your mouse.
Below the menu line is a line of control buttons. These are the primary control buttons for
the interface. Using these buttons you can change mode from [MANUAL] [AUTO]
[MDI] (manual data input). You can also use [FEEDHOLD] or [ABORT] to stop or abort
a programmed move. When you press the [FEEDHOLD] button it changes color and
becomes a [CONTINUE] button. It toggles between running and pausing. Feedhold has
the advantage of being able to restart the program from where you stopped it. When all
else fails press a software E-Stop—the button in the upper right labeled [ESTOP PUSH].
26
There are two columns below the control line. The left side of the screen shows axis
position, feedrate override, and any messages that are sent by the EMC to the operator.
You can add things like current tool number and length, type of position shown, and
offsets in effect by looking under the <View> menu.
Directly below the pop-in area on the right side of the screen is the area that is controlled
by the chosen mode. In [MANUAL] mode it’s configured so that you manually control
the slide movements. You’ll have your choice of “jog” or “incremental” moves using the
same big buttons. In [AUTO] mode it displays a set of buttons that allow you to load a
part program, view the current location and [Run] it. In [MDI] mode it displays a line
where you can enter your command in standard programming code.
FIGURE 2—The screen with BACKPLOT displayed
If you compare the second screen shot with the first you can see that we are in now Auto
mode, a program has been run, and the tool path is being displayed using Backplot.
Notice that the display position numbers have changed color. When you start first load
the EMC program, the slide location position will be displayed in gold. This means that a
homing routine has not been done yet. Once an axis has been homed, the numbers turn
dark green.
To the upper right of the plotting screen is a small window with a pyramid figure that
displays the angle from which you are viewing the tool path. When the EMC is first
started, the default view in the Backplot mode is oriented at (X-27°, Y17°, Z30°,
Zoom=0). These values can be changed by using the sliders underneath the pyramid to
view your program from any angle and at various distances. While running your program
in Backplot mode, keep these values in mind, as they will determine how the program is
27
drawn on the screen. While viewing your tool path from beneath, for example, the
movements may appear to be opposite of how you have defined them in your program.
Feedhold and Feedrate Override
You can operate feedrate override and feedhold in any mode of operation. Override will
change the speed of jogs or feedrate in manual or MDI modes. A feedhold will be
initiated if you click the [FEEDHOLD] button or if you press the pause button on the
keyboard. Once in feedhold, the same actions will return you to the speed the machine
was moving before the feedhold.
You can adjust feedrate override by grabbing the slider with your mouse and dragging it
along the groove. You can also change feedrate a percent at a time by clicking in the
slider’s groove. In auto mode you can also set feed override in 10% increments by
pressing the top row of numbers on your keyboard. The number 1 will set feed rate
override to 10 percent of programmed or jog speed. The number 9 will set 90 percent.
NOTE: Do not enter a value higher than 100 for the Feed Override, as the program will
stop and you will get the error message “axis 0* following error.” (*The number
indicated could be 0, 1, 2 or 3 depending on the axis selected.)
Messages
The message display located under the axis positions is a sort of scratch pad for the EMC.
If there are problems it will report them there. If you try to home or move an axis when
the [ESTOP] button is pressed, you’ll get a message that says something about
commanding motion when the EMC is not ready. If an axis faults out for something like
falling behind, the message pad will show what happened.
If you want to remind yourself to change a tool for example, you can add a line of code to
your program that will display in the message box. Example: (msg, change to tool #3 and
press resume) will display “change to tool #3 and press resume” in the message box. The
“msg,” comma included is the command to make this happen; without “msg,” the
message wouldn’t be displayed in the message box.
To erase messages, simply click the message button at the top of the pad or hold down
[Alt] and press [m].
Manual Mode
Manual mode shows a set of buttons along the bottom of the right-hand column. A green
button labeled “ALL ZERO” has been added to designate the present position as the
home position. I felt that a machine of this type would be simpler to operate if it didn’t
use a machine home position. This button will zero out any offsets and will home all axes
right where they are.
Axis Focus (Active)
Axis focus is important in manual mode. Notice that in Figure 1 above you can see a line
or “groove” around the X-axis position display. This groove says that X is the active axis.
It will be the target for jog moves made with the plus and minus jog buttons. You can
change axis focus by clicking on any other axis display. You can also change axis focus
in manual mode if you press its name key on your keyboard. Case is not important here.
28
[Y] or [y] will shift the focus to the Y-axis. [A] or [a] will shift the focus to the A-axis.
To help you remember which axis will jog when you press the jog buttons, the active axis
name is displayed on them.
Jog Mode
The EMC can jog (move a particular axis) as long as you hold the button down when it is
set for “continuous,” or it can jog for a preset distance when it is set for “incremental.”
You can also jog the active axis by pressing plus [+] or minus [–] keys on the keyboard.
Again, case is not important for keyboard jogs.
The two small buttons between the large jog buttons let you set which kind of jog you
want. When you are in incremental mode, the distance buttons come alive. You can set a
distance by pressing it with the mouse. You can toggle between distances by pressing [i]
or [I] on the keyboard.
Incremental jog has an interesting and often unexpected effect. If you press the jog button
while a jog is in progress, it will add the distance to the position it was at when the
second jog command was issued. Two one-inch jog presses in close succession will not
get you two inches of movement. You have to wait until the first movement is complete
before jogging again.
Jog speed is displayed above the slider. It can be set using the slider, by clicking in the
slider’s groove on the side you want it to move toward, or by clicking on the [Default] or
[Rapid] buttons. This setting only affects the jog move while in manual mode. Once a jog
move is initiated, jog speed has no effect on the jog. As an example of this, say you set
jog mode to incremental and the increment to 1 inch. Once you press the [Jog] button it
will travel that inch at the rate it started.
Keyboard Jogging
When the control is in manual mode you can also control the slides using the keyboard
cursor control arrows. The slides will move in the direction the arrows point, and the Zaxis can be raised or lowered using the [Page Up] or [Page Down] keys. The speed the
slides move at will be determined by the manual feed rate setting.
Yes, you can move the machine around in manual mode. You can even do some tolerable
milling in manual mode, so long as you work a single axis at a time and set jog speed for
the feedrate that your tool, machine, and material need, but the real heart of CNC
machine tool work is the auto mode.
Auto Mode
Sherline’s auto mode displays the typical functions that people come to expect from the
EMC. Along the top are a set of buttons which control what is happening in auto. Below
them is the window that shows the part of the program currently being executed. As the
program runs, the active line shows in white letters on a red background.
The first three buttons, [Open], [Run], and [Pause] do about what you’d expect. [Pause]
will stop the run right where it is. The next button, [Resume], will restart motion. They
are like “feedhold” if used this way. Once [Pause] is pressed and motion has stopped,
[Step] will resume motion and continue it to the end of the current block. Press [Step]
again to get the motion of the next block. Press [Resume] and the interpreter goes back to
29
reading ahead and running the program. The combination of [Pause] and [Step] work a
lot like single block mode on many controllers. The difference is that [Pause] does not let
motion continue to the end of the current block.
Feedrate Override and Auto Mode
The number buttons along the top of the main keyboard will change feed rate whenever
you are in auto mode. Pressing the gravé [`] gets you zero percent feed rate. One through
zero gets you ten through 100 percent feed rate. These keys can be very handy as you
approach a first cut. Move in quickly at 100 percent, throttle back to 10% and toggle
between [Feedhold] and 10% using the keyboard’s pause key. When you are satisfied that
you’ve got it right, hit the zero to the right of nine and go.
Verify
The [Verify] button runs the interpreter through the code without initiating any motion. If
verify finds a problem it will stop the read near the problem block and put up some sort
of message. Most of the time you will be able to figure out the problem with your
program by reading the message given and looking in the program window at the
highlighted line. Some of the messages are not real helpful. Sometimes you will need to
read a line or two ahead of the highlight to see the problem. Occasionally the message
will refer to something well ahead of the highlight line. This often happens if you forget
to end your program with a %, m2, m30 or m60.
Restart
To the right of the program window is a space that will show a set of restart functions.
These pop in whenever a program is aborted or an EStop happens while the interpreter is
running or paused. You can also display or hide these using the view menu.
I’ve got to warn you that [Restart] can be risky. [Restart] reads down through the
program to the restart line. While it does this it sets up its “world model” so that it can
resume right where it stopped, but only if the tool is right where it was. Most of the time,
when we abort or EStop it’s because something went wrong. Perhaps we broke a tool and
want to change it. We switch to manual mode and raise the spindle, change tools, and
assuming that we got the length the same, get ready to go on. If we return the tool to the
same place where the abort was issued, the EMC will work perfectly.
It is possible to move the restart line back or ahead of where the abort happened. If you
press the [Back] or [Ahead] buttons you will see a blue highlight that shows the
relationship between the abort line and the one on which the EMC stopped. By thinking
through what is happening at the time of the restart you can place the tool tip where it
will resume work in an acceptable manner. You will need to think through things like
tool offsets, barriers to motion along a diagonal line, and such before you press the
[Restart] button. A restart is a good time to use feed rate override and the pause key on
your keyboard.
MDI
MDI mode allows you to enter single blocks and have the interpreter execute them as if
they were part of a program—kind of like a one line program. You can execute circles,
30
arcs, lines and such. You can even test sets of program lines by entering one block,
waiting for that motion to end, and then enter the next block.
Below the entry window, there is a listing of all of the current modal codes. You can also
write this list to the message box in any mode if you look under the info menu and select
active g-codes. This listing can be very handy. I often forget to enter a g00 before I
command a motion. If nothing happens I look down there to see if g80 is in effect. G80
stops any motion. If it’s there I remember to issue a block like g00 x0 y0 z0. In MDI you
are entering text from the keyboard so none of the main keys work for commands to the
running machine. [F1] will Estop the control.
Pop-in Editor
To edit a program that is already open, make sure the “Editor” button is active at the top
of the screen. (Clicking on the box next to the word “Editor” will make it turn red,
meaning it is active.) Clicking repeatedly on the work screen toggles between any
functions that are active (box is red) across the top row. In the Editor window you can
edit the g-code for your file. When you open this screen, you will see that a small menu
bar opens above the screen with the usual editing functions to be found under “File,”
“Edit,” etc. With these you can copy and paste within the program. The pop-in editor
does not allow you to copy and paste between programs.
CAUTION! Be very careful when you highlight text when you are writing a
program. If you accidentally hit any key while a line or lines is selected it will delete
the selection. When this happens there is no “undo-oops-back” command. Using the
“File > Save” command often is highly recommended.
The Editor feature is included because it has the ability to number and renumber lines in
the way that the interpreter expects of a file. It will also allow you to cut and paste from
one part of a file to another. You can save your changes and submit them to the EMC
interpreter with the same menu click. You can work on a file in here for a while and then
save and load if mini is in auto mode. If you have been running a file and find that you
need to edit it, that file will be placed in the editor when you click on the editor button on
the top menu.
The newer software has a menu listing for another Linux editor named “Kate.” Kate does
allow for copying and pasting between programs. You can load several and even split the
screen between them. From the “K” menu in the lower left corner of the screen go to
“EMC > G Code Editor.” When you start it and select “Open” you can find all your
stored programs and use "File > Open" to open one. If you highlight a section of text and
use the "Edit > Copy" commands you can then open another program and use the "Edit >
Paste" commands from the menu to paste the lines of code into another program. This
editor does not have the ability to automatically reload the program into the EMC
interpreter after a change. You will need to do that in EMC by selecting the program file
after saving it with Kate.
Backplot
[Backplot] will show the tool path that can be viewed from a chosen direction. “3-D” is
the default. Other choices and controls are displayed along the top and right side of the
31
pop-in. If you are in the middle of a cut when you press one of these control buttons the
machine will pause long enough to re-compute the view.
Along the right side of Backplot is the pop-in that you can display with the [SETUP]
button. This will show a small graphic that tries to show the angle you are viewing the
tool path from. Below it are a series of sliders that allow you to change the angle of view
and the size of the plot. You can rotate the little position angle display with these. They
take effect when you press the [Refresh] button. The [Reset] button removes all of the
paths from the display and readies it for a new run of the program but retains your
settings for that session.
Pop-in Tool
The tool page is pretty much like the others. You can set values here and they become
effective when you press the [Enter] key*. You can’t change tool offsets while the
program is running or when the program is paused. The [Add Tools] and [Remove Tools]
buttons work on the bottom of the tool list. Once a new tool has been added, you can use
it in a program with the usual commands.
*Always use the [Enter/Return] key at the right side of the normal alpha keyboard, not
the [Enter] key at the bottom right of the numeric keypad.
Limit switches
I felt that limit switches would add an unnecessary cost to the system when using stepper
motors with limited torque such as these. They have to be mounted in areas where they
are exposed to chips, oil and coolant creating more problems than they eliminate. The
Sherline mill is fitted with “Hard Stop” screws on the X and Y axes that limit travel.
These stops are the heads of cap screws fitted to the table and base and positioned to stop
a runaway axis without damage. If you make a programming error that would drive the
table into a crash situation by over-traveling, the table will encounter these hard stops
before damaging the leadscrews and nuts.
You could also locate a home position from these hard stops by stalling the stepper
motors against them. Of course you should do this in manual mode and by bringing the
table against the hard stop carefully in slow speed and "buzz" the motor against it. I
personally would find a different way of locating a home position, using the dials on the
handwheels for example, but it is an option for unusual situations
It should also be noted that the hard stop screw would have to be removed from the left
underside of the table in order to have the full nine inches of advertised X-axis travel.
With the stop screw in place travel is about 8.65".
An introduction to Programming and Operating Your
Sherline CNC Vertical Mill
By Joe Martin
Manual vs. CNC
Let’s think about what we have to do to write a program for CNC:
1) Create a spot on your storage system.
32
2) Write a program.
3) Test it for errors using the Backplot program.
4) Dry run the program with the spindle well out of the way so it can’t possibly
crash.
5) Accurately align the machine with the work so they work in unison when the
program is run.
Push the button and have a cup of coffee while your little Sherline just works its butt off
for you making good parts.
When you think about this, it has the same steps as to do it manually. Compare:
1) Make some special tooling to hold the special shape. With CNC you can hold
raw stock in a vise and machine the shape you need.
2) We’d have to store the special tools in case we wanted to make another one.
3) You’ll make a lot of scrap with a manual machine if you don’t double check
your work before making the first cut, and you will not have a computer to help
you as you do with EMC.
4) No matter how you do it, you always have to line up the work to the machine.
5) Don’t put the coffee on yet because your real work has just begun while our
boy with the CNC is pouring a second cup and making 7th part of ten pieces. (Oh,
how I wish it could be this easy at the start!)
Using “Backplot” to check your program
1) To work with any existing programs we have to be in the [AUTO] mode. With power
to the stepper motors turned off [Open] the existing program called “3dtest.ngc.” This file
comes with EMC.
2) Open the [BACKPLOT] program that can be found on the upper line and a blank
section will appear in the Pop-in section. The [Backplot] feature will allow you to
visually check a program without actually running the stepper motors. Right clicking
your mouse controls the program that is viewed in this section of the control panel. You
can toggle between the editor and the backplot easily. We now have the perfect setup to
learn CNC and it all fits on a single desktop. You can view and edit your program or
view the moves the spindle will make while your program is running.
3) Now that we have a program loaded and the Backplot program running, let’s take a
break and test our setup. Make sure that [ESTOP] is active with the button highlighted
and execute [Run].
4) Observe that the programmed moves can be viewed in the backplot box and the
viewing area can be controlled with a variety of controls. This is very useful in checking
out the programs you’ll be writing in the upcoming lessons. The line of the program that
is highlighted in red in the lower area of the control panel is the line of code that is being
processed by the control as the computer runs the program. Note that the EMC program
is processing more than a single line of code at the same time; therefore, this line should
only be considered "approximate."
33
How to make a file for our programs
It’s possible to create a new file and have them end up in the wrong folder never to be
seen again, and if you use this method you will always have your new programs in the
proper folder. If you are using a computer supplied by Sherline, you’ll find the file called
“0-new.” The instructions in sections D) and E) below describe how to change
“3dtest.ngc” to “0-new.” Since Sherline owners will have this file already provided for
them, they can skip sections D) and E) when they come to them and go on to section
1) To create a new file or work with any existing programs remember you have to be in
the [AUTO] mode. Notice that a new line of commands appears along the bottom in this
mode. The [Open] button is located in the along this row. Note: the method I’m
describing in A) to E) below is to set up your computer for future use and isn’t the
necessary steps you’ll use in the future.
A) With power to the stepper motors turned off [Open] the existing program
called “3dtest.ngc.”*
*This file comes with EMC. If you are using a computer supplied by Sherline,
you should instead open the file called “0-new.” The instructions in sections D)
and E) below describe how to change “3dtest.ngc” to “0-new.” Since Sherline
owners will have this file already provided for them, they can skip sections D)
and E) when they come to them and go on to section 2).
B) Go to the Pop-in [Editor] command and open along the top row.
C) The window will display the entire program.
D) For those of you who do not have a Sherline-supplied computer we are now
going to create a file we will call “0-new.” (If you have a Sherline computer with
the “0-new” file already on it, open it and go to section 2) below.) First go back to
the [Editor] window by right-clicking your mouse. By having a “0” as the first
character of the file name it will always keep this file at the beginning of the
program list. This makes it easy to find, because you are going to use it again and
again. From the [Edit] window, use [File] then [Save as] (located along the top of
the edit window) to save our existing program as “0-new.”
E) Next, highlight (with the mouse button held down drag the cursor across the
entire area you wish to highlight) and delete (press enter) the existing program
with your mouse. Replace that program by typing “Save as another file name.”
This will remind you to only use the “0-new” program to set yourself up for
creating a new program. Use the [File>Save] command. Remember, to make any
changes permanent you must save the changes before closing the program.
2) We’ll now use the [Save As] command to save the “0-new” file with the new name
“test-g02”. By using the [Save As] command you also leave the “0-new” program as is to
use again. You can create your own files and name these files as you wish from this point
on. Note: “test-g02” is the first program you’ll write. Program files are saved in the
directory called “/home/Sherline/gcode”. In the EMC, the programs will be saved here
by default. HANDY HINT: You can always look at all the program files by clicking on
the “Home” icon on the desktop. From here click on the folder entitled “gcode.” You will
find instructions for saving them to a floppy a few paragraphs further on.
34
3) You have to get the new program loaded into the control (machine) in order to use it.
4) To accomplish this first use [File] [Open] to open your new “test-g02” program. The
program will now be loaded in the control panel with the program name displayed.
All of this BS isn’t as bad as it seems and you will quickly create programs using this
information along with “0-new.”
Maintaining your EMC programs directory
Many times you will create a number of G-code files that are similar or for testing use.
After a while these files can accumulate into a large repository that makes it difficult to
find the one you are looking for. If you wish to delete a file the easiest way to do so is to
click the “Home” icon on the desktop and find the folder called “gcode.” This is the
default location of G-code files created in EMC. Find the file(s) you wish to delete. Right
click on them and then left click on the [Delete] option. This will permanently delete the
program selected. Take great caution when deleting files! You do not want to
accidentally delete a valued file.
______________________________________________________________________
35
Part Two
Programming Sherline CNC Machines
with EMC
Although there is quite a bit of well-written instruction on how to program on the Linux
CNC site, I believe you should only go there to learn beyond the limits of my
instructions. Having too many instructors on a subject that you know nothing about isn’t
a good idea at this time. At the end of my instructions there are lists of the many words
and commands available to you taken from the Linux EMC site; however, there isn’t any
reason to remember them now. I want you to learn them as you use them. The commands
and words that I’ll be using are so basic to writing code that they’ll soon become a new
language.
UPDATE —July, 2005: Note: I recently went back to the EMC website at
http://www.linuxcnc.org/ and was very pleased to find many improvements have been
made since I first wrote these instructions. It’s much better organized now, and I believe
after you get the basic concepts from my instructions about how CNC g-codes work, it
would be to your advantage to go there and learn about the addition of the many canned
cycles that are now available to EMC users. A new complete list of g-codes is available
at http://emc.sourceforge.net/Handbook/index.html. I take my hat off to the EMC group
for making these much needed improvements.
Print a copy of these instructions
Although you could jump between the control screen on your monitor and the
instructions, it would be a cumbersome way to work. You can print a copy of these
instructions from the CD using any computer with a printer hooked up to it, or you can
print a copy from your Linux computer by unplugging the servo driver connector from
the parallel port and plugging in a printer instead.
To make it easier and to save paper, we have saved just the portion of the instructions that
refers to the programming as a separate file you can print out. You have your choice of
formats: They are called CNCprint.doc (MS Word) or CNCprint.pdf (Adobe
Acrobat*). You can also open the instructions on Sherline’s web site at
www.sherline.com/CNCinstructions.htm and print only the pages starting at the
beginning of Part 2. (Note: Later editions of these files may include a version number in
the name; for example, “CNCprint4.pdf.”)
*Your Linux computer already has a program installed that will allow you to read .pdf
files by clicking on them. To view .pdf files on your Windows® computer, a copy of the
free program Acrobat Reader will need to be installed. Clicking on a .pdf file should
cause that program to open automatically. If you don’t have it or want to get the latest
version, go to www.adobe.com/products/acrobat/readstep.html.
36
Inch vs. metric dimensions in G-Code
Because my instructions have been written using the inch dimension system, work with
the inch version of EMC when using my examples at this time. This will slightly decrease
actual table movements on metric machines. The g20 and g21 conversion command will
only work if you load the EMC version that is appropriate with your leadscrews. Should
you wish to use metric dimensions to program your machine, even though it has an inch
leadscrew, you can do so by entering the code g21 in place of the g20 code when writing
the program for your part. G20 indicates inch increments, while entering g21 indicates
you will be using metric increments. The program will automatically make the translation
for you. You can also use inch dimensions on a machine with metric leadscrews by using
the g20 code instead of g21 once the proper version of the EMC has been opened.
If you use the g20 or g21 command to change measurement systems, don't forget to clear
any previously entered numbers from the tools table. Then re-enter the tool size in the
appropriate measurement system for your current program. If you don't, you will end up
with a program that has tool offsets entered in a different measurement system than the
g20 or g21 command calls for. This can give you an error message and the program may
not run.
Let the BS end and the programming begin
From this point on, you have to learn programming at your CNC system. You can’t learn
how to control these systems in your favorite easy chair; therefore, you should take a
printed copy of “Part Two” to your CNC system and enter, test and understand each
sample program before going on to the next. Write a few similar programs, with each
being different enough to make it challenging and constantly test yourself as you go. No
shortcuts!
Are you ready?
About now I’d be “chomping at the bit” to see something happen, so lets do something
the best manual machinist couldn’t do to start. Hell, anyone can cut a straight a straight
line so let’s make a circle. With the stepper motor controller power switched off,
manually crank the handles and approximately center the X-, Y- and Z-axes. Leave the
power off to the stepper motors until we get the program all checked out with Ray
Henry’s backplot command. Ray Henry has been a sparkplug for the EMC group for
some time now and we all owe him a debt of gratitude.
G-code programming
These are the basic g-codes that you’ll be working with. There is a complete listing of
them at the end of this section copied from the www.linuxCNC.org site. There isn’t any
reason for you to remember them all at this time, because I want you to thoroughly learn
them as you use them; however, you can get a general idea of how the system works by
reading them now. They are quite simple. Remember that modal g-codes remain in effect
until the control receives a new g-code that over-rides the present code. Modal g-codes
37
control function, direction or speed and, in general, cannot be used in the same line of
code with other modal g-codes for obvious reasons.
g00 rapid positioning
g01 linear interpolation
g02 circular/helical interpolation (clockwise)
g03 circular/helical interpolation (c-clockwise)
g04 dwell
g10 coordinate system origin setting
g17 xy plane selection
g18 xz plane selection
g19 yz plane selection
g20 inch system selection
g21 millimeter system selection
g40 cancel cutter diameter compensation
g41 start cutter diameter compensation left
g42 start cutter diameter compensation right
g43 start tool length compensation
g49 cancel tool length compensation
g90 absolute distance mode
g91 incremental distance mode
There are no erasers in the machine trades
One other quick thing to note, it should be obvious that I could have provided a disk with
all the examples typed in or to be downloaded, but accurately typing in a program is as
much a part of learning CNC as making chips. When you misspell a word in a letter, the
reader of the letter usually knows what you were trying to say and will not even notice it.
In the world of robots, our robots can self-destruct trying to carry out your foolish typing
error. This kind of typing requires them same precision as machining. There are no
erasers in the machine trades. Only people who express themselves with their mouths and
writings have the use of this marvelous tool. Machinists express themselves with their
work, and that’s the way I like it.
In this exercise the home position is going to be where the tables were located when the
EMC program was turned on, which is why I had you center the machine slides and is
called x0,y0 and z0. The X-axis is the table that will move to your left when it moves in a
positive direction. The x0, y0 and z0 is also designated in the backplot box with arrows
pointing towards the positive direction away from this position. No more excuses, we’re
going to program that circle I promised you. Note: Although the EMC program doesn’t
need the “0” after the “g” in g00 or g01 I’ll use them because they are the designations all
popular CNC systems use. Also, I prefer lower case letters because you are less likely to
make errors and mix them with numbers. The capital letter O and the number 0 can be
difficult with some fonts and are located close together on any keyboard. You are not
writing a letter when you program, and it has to be accurate.
38
Circle program
Note: In these instructions, the code you should retype into your program will always
shown in bold face red type.
The entire program:
%
(g02 circle program)
g01 g20 g40 g49 g90 x0 y0 z0 f2
g02 x0 y0 i-.5 j0
g01 g90 x0 y0 z0 f2
%
1) % –Always start a new program with a % sign. This informs our robot that a
program is coming in. Each time you press [Enter], the program will start a new
line, so [ENTER] it is, and we’re off and running.
2) (g02 circle program) –Words in parentheses are not part of program and are used
to help the operators quickly understand the program. You can enter notes into a
program at any point to remind yourself or another operator in the future why the
upcoming code was entered.
3) Note: The g20, g40, g49 commands are not totally necessary for this program to
run. They are added to protect your program from being polluted by commands that
may have been active in previous programs and never canceled out. About the only
one of this group that could eliminate a potential problem is the g20 which could
keep your inch program from running in metric if a g21 was left active. I really
didn’t want to get into this subject this early in the instructions; however, if you
were using a computer that other people use it could be a problem so I believed I
should mention it and I’ll only do so in this first programming example.
4) g01 g20 g40 g49 g90 x0 y0 z0 f2 –What we just ordered our robot to do is go to the
home position if it’s not already there.
A) g01–Enters a mode where the feed (speed) is controlled by “f” which can be
entered. Also note that the slow feed of f2 was entered so you could fully
appreciate just what the machine slides do to generate a circle. The feed could
be set for a faster rate for the backplot test and slowed down for the machine
test if desired.)
B) g20–Orders the machine to use the inch measurement system. Metric machine
owners will use a g21 in place of the g20.
C) g40–-Cancels any unwanted tool diameter compensation that may have been
left active from previous run programs.
D) g49–Cancels any unwanted tool length compensation that may have been left
active from previous run programs
E) g90–Orders the machine to use the absolute coordinate system where the
position will always be referenced from a zero point. Again, you can zero the
axis by going to [Pop In] [Offset].
39
F) X0, y0, z0 is self evident. If the slides weren’t in the 0 position they would
have moved to it.
This is the basic information that all programs should start with. If I had entered a g00
command to start with (orders the machine to move to the programmed position at fastest
speed) it would be a quicker but one that can be more risky to start with. Modern CNC
machines can perform g00 moves at speeds of 1400 inches a minute (35mpm), and
you’re making a mistake by not taking advantage of this fact, but we’re not pros at this
time and I want you to learn about feeds. Hit the [ENTER] key.
5) g02 x0 y0 z0 i-.5 j0 – This line is the code that is going to actually produce the x y
movements to create that circle we have been talking about. In this case, all the
previous commands are still in effect except the g02 is replacing the g01.
A) g02 is ordering our robot to cut a circle or start an arc with a clockwise (CW)
move. For our faithful robot to carry out this order it needs more information
or it’s going to start complaining and sending you nasty little notes and refuse
to work. Remember that the g02 will remain in effect until a g01 is called for.
B) The g02 the program needs the x, y position entered as to where this arc will
end, and since we are creating a circle it obviously will end where it started so
the present position is entered.
C) Here are a couple of new commands; i and j, and they are used to describe the
center location of our circle. These dimensions are given as the actual distance
the center is located from the present position. It is very important to
understand that our present position is not the center of this circle and only a
starting point for this circle to be created. The i represents where the center of
the circle falls on the x-axis and the j represents the y-axis.
I would also like to add at this time that the distances calculated and entered for computer
generated shapes have to be extremely accurate, and a 0.0002″ error could stop your
program from running. This doesn’t have anything to do with the accuracy you need; it
pertains to the accuracy the computer needs to calculate the many points it creates to
generate the x y movements for this one circle. This shouldn’t be any problem because of
the low cost calculators we all have today that figure things to many decimal places. Hit
[ENTER]. (This is the last time for the [ENTER] command to be instructed. From now
on you will hit [Enter] at the end of each line of code.)
6) g01 g90 x0 y0 z0 f2–I always add a line of code with a g01 or g00 and a x,y,z to
return to the home position. The “g” commands stay in effect until they are
overwritten by another g command. In this case it would have left the control in a
circle command if we didn’t add this line of code which wouldn’t be a good
practice.
7) % -To inform our robot that this is the end of our simple program to do a very
complex thing we enter a % just as we did to start the program.
8) Now we have to load this program for your machine to run. [File] [Save and Load]
In this case we are not ready for prime time, and we are going to check our program
with [Pop In] [Backplot].
40
9) One more check –the program should look like this:
%
(circle g02)
g01 g90 x0 y0 z0 f2
g02 x0 y0 i-.500 j0
g01 g90 x0 y0 z0 f2
%
10) Go for it, click on [Run]. The backplot program should start tracing the path the
spindle will travel in relation to the work. If you got one of those little messages and
it didn’t run, check for typing errors and correct them. Right-click [Editor] [file]
then [Save and Load] [Run] until it works.
11) The time has finally come to watch this little beauty in action, so turn on the
machine control and “let her rip.” Notice how the slides are constantly changing
speeds as each axis reaches its apex and changes direction. The circle is also being
generated in the CW direction as the g02 requires. Run this little program several
times and take the time to really understand what’s going on. From the control
panel you can single step the program through and run things until you’re bored.
You had your fun and it’s time to go to school again
Now guys and girls, it’s time to go back as many times as it is necessary until you are
absolutely positive you know exactly what every letter of your program does. I’m not
looking over your shoulder, and the only way you can act foolish is by being on page 10
when you should be on page 3.
What a difference a minus sign can make
The first thing I want you to learn is how important that minus sign can be. (Also, a
misplaced decimal point can easily cause a catastrophic machine event.) First, turn off the
machine because there isn’t any sense in having it run while we’re doing this exercise.
It’d also be distracting. Run your existing program through once again and generate the
circle you started with. Leave the circle there and don’t [Reset] until we are done with
this entire exercise. Right-click to Edit your program and the only thing I want you to do
is remove the minus sign from the i value in the g02 command. [Save and Load] and
[Run]. I’ll bet you didn’t think it was going to do that! Just think what could have
happened to that expensive fixture if you were controlling a 30HP mill. A quick way to
the unemployment line. I’m now going to give you the golden rule #1 of any CNC shop.
Don’t ever press the green [Start] button on a CNC machine
unless you know exactly what the machine will do BEFORE you
PRESS IT!
Now let’s take a closer look at that minus change we made and we’ll see what happened
is really obvious. By changing the “i” to a positive number the center of the radius is
now moved to the positive side of our zero starting point, which in this case is a total
distance of 1". The g02 command still went in a CW direction and the only difference is
41
that the circle was generated on the positive side of the X plane. Are you up for your first
test? You better be because I didn’t write all this stuff for my own enjoyment.
From what I explained to this point, you should be able generate a 4-leaf clover on the
backplot screen. Don’t forget to use save and reload as you make these changes. You’re
on your own.
Figure 1
If you’re reading this, I’ll assume you passed the test, so now take your second test by
erasing your program with the backspace key and doing the entire exercise over from
memory.
Meet Millie
Think about what you accomplished at this point. You’re beginning to understand how
we humans can order our robot around. I think we should give our little robot a name.
Seeing it’s a mill we’re working with and I’m a male, I think I’ll call mine Millie. It will
be the only thing with a female name in my lifetime that I stand a chance of controlling. I
really want you to know the stuff I taught you blindfolded because we are heading for the
hard, oops, I mean interesting part.
I’m buying
I’m a little bored with this exercise myself so let’s drop over to route g41 and see what’s
going on. The programmers that reside on g41 are a little on the snobby side because they
think they have some special talent that us regular guys can never learn. That was
probably true when they learned it, but they didn’t have Joe Martin teaching them. In
Joe’s class no one is left behind, and let me promise you this guys, we are going move
into their neighborhood so fast they will think we always lived there. But for the hell of
it, let’s stop by their fancy cocktail lounge and have a beer so they can get used to us. I’m
buying.
Homing your machine
Now would be a good time to slip something in about “home position,” which is the
actual x, y and z position the machine is in when you start to run your program. I will
42
usually have the zero points in the same location as they are on the drawing, which makes
the program easier to write without errors; however, it is seldom the actual position you’d
want your machine to be in to load or unload parts or check dimensions. The best way
I’ve found to determine the home position is to first locate the zero position. Jog the
slides to the approximate zero position and then move them manually with the
handwheels (power to the drivers turned off) to the exact position where your cut will
start. Zero the control's readout by using the "zero all axes" button. With driver power
switched back on, the slides can then be moved to a position that you believe would be a
good home position using the incremental jog feature or the MDI program. It’s a good
idea to make these whole numbers such as x2 (or 50 mm), y2 and z2 because you’ll have
to type these in when writing your program. You’ll have to be careful of having tools
loaded in the spindle and manually calling a zero position before the program has a tool
length offset loaded. This last warning will make much more sense later on in the
instructions.
Tool height offsets
Before we get too involved in the more complex cutter diameter programming, I want
you to learn how to deal with the difference in tool lengths. It is obviously simpler to
have a single zero point for all tools, and that is what the EMC program allows you to do.
The length and diameter of each individual tool is stored in a file called “Tools,” located
along the top row of the control panel. The tool length is usually called up in the first zaxis move using each individual tool by entering a g43 h1,2,3,--. The g43 tells the
computer to use the tool length (h) stored in the line (1,2,3,---) of the tool data file. A g49
is entered when the z-axis is brought back to its home position to cancel out the tool
length compensation that was called up when you first started using the tool.
From a practical standpoint, I like to make the shoulder located behind the ¾-16 spindle
nose thread the zero point on the Sherline mill and use screw-on Sherline tool holders.
This allows you to measure the tool length directly with calipers by measuring the overall
length of the holder with the tool mounted. Also remember that the home stopping
position for the z-axis shouldn’t be zero. It should be a positive number that allows you to
change the tool if necessary. The x0, y0 and z0 position should be chosen carefully and
be related to the part that is being programmed, not to a convenient place to change tools.
Write a couple of lines of code with and without the tool length compensation to test
what you have just learned. Run it using the backplot to fully understand it before going
on, and, above all, always remember to cancel the tool length compensation after using it.
Time to get serious
Let’s think about just what g40, g41 and g42 does. To begin with g41 (g42 is the opposite
of g41) will locate the spindle to the left of the programmed edge that you want to
machine according to the d (tool dia.) amount entered into the tool data table. G40 simply
cancels the g41 or g42 commands.
Computers can keep you from ruining your part
These commands allow you to put the actual dimensions of the part you want directly
into the program and then it will take the diameter that you entered into a [Tools] file and
automatically correct the path of the cutter so that the edge of the cutter is always located
43
on the edge on the part. Your computer will be making thousands of calculations a
second to do this, and old Millie will just bust her hump for you to make this happen if
you follow their rules. If you don’t, they’ll start sending you those nasty little messages
again, but look at it as a blessing. They’ll keep you from wrecking your part.
Another thing to keep in mind is that one of the great benefits of the tool offset
commands is being able to use end mills with slightly different diameters without having
to calculate all new tangent points. Before CNC, when NC was the only system available,
there was a surplus of used end mills on the market that had not been re-sharpened
because it was cheaper to scrap out dull end mills without re-sharpening them than to
write long complex programs to account for their smaller diameter.
Don’t ask for impossible
The first thing you have to learn about using the g41 or g42 cutter comp commands is
that you can’t ask your machine to do the impossible. What is impossible is cutting an
inside “V” with an end-mill.
Figure 2
If you firmly imbed this into your mind, you’ll save the many hours of wasted time that I
spent learning it. Of course I knew that this is impossible, but I kept asking my computer
to do it when I was entering the cutter offset mode. As soon as a g41 or g42 is entered
into the program you can’t ask your machine to cut “V” shapes without an arc being
programmed that is at least the radius of the cutter you are using. What confused me was
the cutter diameter that was retrieved with the d-command had an effect on whether you
would or would not have an error. I believe I truly understand it now and had to rewrite
several pages of garbage I wrote with confusing rules.
44
Safety first
I believe you shouldn’t approach the work at this time in a rapid g00 mode for safety
reasons; therefore, all my examples will include a short section of controlled feed rates
before the point of contact is reached. My program examples will always be complete
and will run on the backplot program that comes with your system. I have yet to find a
program that checks out with this program that wouldn’t run on the Sherline mill if the
slides were located in the proper position before the program was run. The more I work
with the EMC program the more I like it.
Flying Sherline Airlines requires you to learn how to land before flying
The whole trick in using g41 or g42 is getting to the starting point in a very specific
manner. Also, remember that our computer is very smart and looks ahead at what you
plan to do when you enter cutter comp. If you ask it to do the impossible, it will send you
a message. What we want to accomplish is approach the starting point in two separate
moves so that we are coming into the part like a plane on final approach to an airport.
The plane flies to the first point, where it lowers it landing gear (g41—a move where the
cutter comp is entered during the move) and feeds (g01) to the final landing point with its
wheels (cutter) in position to land. Come in too steep and you’ll create a deep V cut that
is impossible to machine. (See Figure 2.)
You can overcome this error by programming a 90° radius cut to the part. Of course, the
programmed radius must be larger than the radius of your cutter. To think of a
programmed move in aircraft terms you are “flaring out” for touchdown. This has a
second advantage from a machining standpoint of not leaving a slight undercut that’s
created when a cutter is brought up to edge and immediately makes a sharp turn. This
undercut is caused by cutter deflection.
The coming programming examples don’t use this method of bringing the cutter up to the
part because it wasn’t necessary in my examples. In the real world, this will be a problem
that you’ll regularly encounter, and you’ll have to use every trick in the book to produce
the parts that are needed.
For the time being, remember that the closer you align your cutter (aircraft) with the
directional edge that you want to machine (runway) the better the landing. Remember, in
the world of CNC there is no gravity, and you can touch down any way you please.
Let’s go back and add g41 to the circle program. Modify your circle program to read like
this. Refer to the drawings with examples in this section.
The entire program:
%
(circle using g40, g41, g42)
g00 g90 g40 x1 y1 z1
g42 d1 x.5 y1
x0
z0
g01 z-.3 f10
g03 x0 y1 i0 j-.5
g00 z1
45
g40 x1 y1 z1
%
Now I’ll go through the program one line at a time
Note: Before this program can be run the tool offset has to be entered. Go to [TOOLS]
and enter 0.250" (6.4 mm) for the tool length, and 0.375" (8.4 mm) for the tool diameter.
You must use the [Enter] key after entering each change in order for the change to be
entered into the table. Close page.
1) % –Last time—Start program
2) (circle using g40, g41, g42) –Last time—Program Name
3) g00 g90 g40 x1 y1 z1 –Home
4) g42 d1 x.5 y1 –End Mill (aircraft) approaches part as tool compensation is
entered (gear down). d1 will define the offset as it moves to this new g42
position. We’re still traveling too fast for landing.
5) x0 – We’re directly above the touchdown area and come to a halt.
6) z0 – Fortunately we’re flying the new Osprey and they can come straight
down.
7) g01 z-.3 f10 –Landing speed and touchdown from a vertical plane.
8) g03 x0 y1 i0 j-.5 –We cut a quick circle just like last time and we’re out of
here.
9) g00 z1 –Straight up
10) g40 x1 y1 z1 –And home.
11) % –Park it and have a coffee. Good flight!
The diameter was generated as before, but this time the final size of this diameter will be
controlled by the diameter entered in to the d1 location. By entering a diameter larger
than the actual tool, which is 0.375", we are assured that the diameter will not come out
undersize, because it keeps the spindle farther away from the finished edge. This can give
you the opportunity to take a second pass and allow you to bring it accurately to size by
changing the d1 value. You have to admit, I’m a clever old bastard.
Rectangle with cutter compensation
I think it’s a good time to take a break from circles and cut something straight before you
get motion sickness. Create a new file for this flight. How about a nice simple rectangle
with cutter comp of course? The material we’ll be serving today is 1" x 1" x 2" (50 mm x
50 mm) 6061 T6 aluminum, and our cutting speed will be 6 IPM. In the event of a crash,
prepare to pick up your paycheck on the way out the door. Have a nice flight.
On this flight we are going to take a couple of quick passes around our 2 inch square
block and machine a 0.150" boss on it to 1.800" square with a 0.375" end mill.
46
Figure 3
The entire program:
%
(cut rectangle with cutter comp)
g00 g90 g40 x1 y0 z1
z-.140
y.090
g41 d1 x.5
g01 x0 f10
x-1.910
y1.910
x-.090
y.100 z-.150
x-1.900
y1.900
x-.100
y.100
x-.200 y-.200
g00 g40 z1
x1 y0 z1
%
Nothing worth commenting about in that program except that my final move before
canceling cutter comp was to eliminate a burr that would have formed if I had gone
straight out, and you should be able to figure rest it out yourself. What you can do is set
the value of d1 at a very small diameter and run the program through. Then set the d1 at
the true diameter of the cutter used and you can see the shape of the part and then the
cutter path followed using g41. Notice how the machine goes around sharp corners. Neat!
47
This isn’t a bad idea to use throughout these problems to help you better understand the
process.
Planes that don’t fly
In the CNC world there are three different planes. They come into play when we want
our computer to do circular interpolation in a vertical plane. With this being the case,
then either the x or y coordinate will have to be predominate with the Z-axis. We can
control these with the g17 (x,y) g18 (x, z) and g19 (y, z) inputs. When we are working in
these vertical planes generating arcs and circles, the z offset for the arc center point will
be controlled by the k input, again designating the offset in the z direction given as an
incremental value. Got that?
Here is an interesting little program I wrote:
The atomic circle program
Figure 4
The entire program:
%
(atomic circle)
g90 g17 g40 g00 x0 y0 z0
g03 x0 y0 i0 j1 f100
g02 x0 y0 i0 j-1
g03 x0 y0 i1 j0
g03 x0 y0 i-1 j0
g18 g03 x0 z0 i0 k1
g02 x0 z0 i0 k-1
g03 x0 z0 i1 k0
48
g02 x0 z0 i-1 k0
g19 g03 y0 z0 j0 k1
g03 y0 z0 j0 k-1
g02 y0 z0 j1 k0
g03 y0 z0 j-1 k0
g90 g17 g40 g00 x0 y0 z0
%
Run it on the backplot program. Millie could also run it, but you’ll have to change the
f100 feed program to f12 so Millie can handle it. Be sure the slides are located in a
position where the slides can be moved two inches (50mm) in every direction. Single step
this program through and again be sure you are positive that you can understand every
move made so well that you can explain to someone what the move is and why it is going
to make it this or that way before going on. Our class is very understanding and we are all
going to wait for you while you go back and catch up, but don’t let it happen again.
The Great Race
Instead of R/C, let’s go PC aircraft racing. We'll watch the race using the backplot
program. First, set the tool diameter to 0.600" in d1. Next, we'll write a short program
that will lay out a triangular course. Our racing aircraft will be a micro delta aircraft that
has strange flying characteristics allowing it to fly forward or backward in a nose down
attitude. (Sometimes it just takes a good imagination.) Racing rules state that it can only
go around the pylons by turning left during the race. Cutter comp will make this easy
because it will automatically calculate the tangent points needed to run this program. By
juggling the turn-in points we can shorten the course, thereby lowering the time. There’ll
be more rules but first lay out a triangular pylon race course. The vertical lines are the
pylon marks. The start finish line is included, and the program will be designed to lay the
course out at the beginning of each new race.
Figure 5
The entire program:
49
%
(EMC race course)
(Set tool diameter D1 to .600)
g00 g17 g40 g90 x-1 y1 z0
g01 y.5 f100
z.5
z0
x-4 y1
z.5
z0
x-1 y1.5
z.5
z0
y.5
g00 x-1.6 y.8
g01 y1.8 f100
(course complete)
(Taxi to starting line)
x-1.6 y1.3 f15
m00
This will pause the program while you get ready to set your stop watch. To start the race
you’ll have to use [Resume] button because the [Run] button will not restart the program
when it is in a “paused” mode caused by the m00. Now for the race…
(Use resume button to start race)
x-2 f6
x-4 y1.4 z.5 f10
g03 x-4 y.6 i0 j-.4
g01 g42 d1 x-3 y.5 f20
x-2
x-1 y.5
y1.5
(lap 2)
x-4 y1 f25
x-1 y.5
y1.5
(lap 3)
x-4 y1 f30
(top speed)
x-1.123 y.578
50
y1.373
(lap 4)
x-3.862 y.961
x-1.123 y.578
y1.373
(lap 5)
x-3.862 y.961
x-1.123 y.578
y1.373
x-1.6
(race over)
g40 x-3.5 z1
x-4 y1.5
g03 x-4 y.5 i0 j-.5
g01 g90 x-2
g18 g02 x-2 z1 i0 k1.5
g01 g90 g17 x2
g02 x2 y-.5 i0 j-.5
g01 x-2 z0 f20
x-2.5 z.15 f15
x-3 z0 f10
x-3.2 z.1 f5
x-3.4 z0
x-3.6 z.05
x-3.7 z0
g03 x-3.7 y-.9 i0 j-.2
g01 g90 x-1 f25
g03 x-.5 y-.4 i0 j.5 f15
g01 y.5
g03 x-1 y1 i-.5 j0
g40 g90 g00 x-1 y1 z0
%
The same program with comments from the pilot:
x-2 f6 –Gaining airspeed and lift-off
x-4 y1.4 z.5 f10 –Climbing out and headed for turn 1
g03 x-4 y.6 i0 j-.4 –Large radius turn to prevent stall
g01 g42 d1 x-3 y.5 f20 –Turn on navigation aid to help in turns
x-2 –2nd point for entering g42
x-1 y.5 –Turn 2 point
y1.5 –Turn 3 point
51
(lap 2)
x-4 y1 f25 –More speed and back to turn 1
x-1 y.5 –Turn 2 point
y1.5 –Turn 3 point
(lap 3)
x-4 y1 f30 –We’re at top speed headed for 1
(top speed)
x-1.123 y.578 –We tighten up the course for the rest a race
Figure 6
I cheated and used AutoCad®…
y1.373
(lap 4)
x-3.862 y.961
x-1.123 y.578
y1.373
(lap 5)
x-3.862 y.961
x-1.123 y.578
y1.373
x-1.6
(race over) –We won
g40 x-3.5 z1 –Turn off the navigational aid and climb out
x-4 y1.5
g03 x-4 y.5 i0 j-.5 – A nice lazy fast turn
g01 g90 x-2
g18 g02 x-2 z1 i0 k1.5 –We change planes and do a victory loop
g01 g90 g17 x2 –Enter the landing pattern back in x, y plane
g02 x2 y-.5 i0 j-.5 –Turn onto final landing approach
52
g01 x-2 z0 f20 –Throttle back, oops, dam it (bounce)
x-2.5 z.15 f15 –Flare it out, dummy
x-3 z0 f10 –Damn, right in front of everyone
x-3.2 z.1 f5 –I give up. I never did like tail-draggers
x-3.4 z0
x-3.6 z.05 –At least I’m still alive
x-3.7 z-.01 –I think I dented their runway
z0
g03 x-3.7 y-.9 i0 j-.2 –Let’s get out of here before they remember me for that
lousy landing
g01 g90 x-1 f25 –A nice fast taxi home
g03 x-.5 y-.4 i0 j.5 f15
g01 y.5
g03 x-1 y1 i-.5 j0
g40 g90 g00 x-1 y1 z0 –Home at last. I wonder if they’ll remember my lousy
landing more than our win
%
NOTE: For those who have purchased the complete CNC system with computer,
this program has been added to the “gcode” folder as “TheGreatRace.ngc” so that
you can open it and test run it without having to retype everything.
Your homework assignment is to figure out this program that I just spent more time on
than I care to admit. There isn’t anything new in it, and you have to understand all the
code used. It may be a little “far out” but it is easy to follow if you know about aircraft.
Your next assignment is to see if you can lower my time from leaving the starting line
until the race is over time is displayed. After lap 2 is completed, the turn-in points are the
only thing you have to work with, and you can’t change the feed-speed or the feed
override on the panel.
My time was an astounding 1 min 42.7 sec. Your job—lower it.
Test two
Up until now all you have done is copy my examples into your computer, and you’re
probably thinking this CNC stuff really isn’t that hard after all. It’s time to bust your
bubble before you get a big head and become a pain.
53
Figure 7
I want you to write a complete program on your own to profile this part. To pass the test,
you must use cutter comp. I have taught you all the fundamentals to write this program,
and the only suggestion I will make is to test the program a segment at a time as you
write it. That’s the great advantage of having Ray Henry’s backplot program to work
with.
Change a couple of dimensions and make one end square and take another test.
There isn’t any sense in entering the next section unless you can easily write these
programs. If not, go through that section again and again until it is second nature.
Back to school
We’re on the move again and leaving route g41 for a while, but I’m sure we’ll return. We
are headed back to school for a refresher class on trigonometry, more commonly called
trig. Today all you need is a $10 calculator that has trig functions or a hook-up to the
Internet where they have a site that will solve your problems instantly by entering any
two known sides or a side and an angle other than 90°.
http://www.pagetutor.com/trigcalc/trig.html
It just doesn’t get any easier than this, or you can use the formulas below and a
calculator. All you have to enter are any two known things about the right triangle you
want to solve other than the 90-degree angle which is always present.
54
Basic Trigonometric Functions
Also: c²=a²+b² c=√(a²+b²) a=√(c²-b²) b=√(c²-a²)
Figure 8
When programmers solve for tangent points, they usually start off knowing the
hypotenuse of the triangle they are working with, because it is the radius of the arc of
which they are solving for the start and stop points.
The hardest part of this part of the course isn’t solving a right triangle. It’s finding the
correct right triangle to solve to give you the answer to determine your tangent
coordinates that will determine the start and stop points of an arc. You’ll remember that I
told you that these points must be given to an accuracy of four decimal places in order to
work in unison with the computer. It has nothing to do with the accuracy you require, but
only with what our loyal computer requires.
I dug out my old calculator to solve these problems and then checked my answers against
what I had already calculated in AutoCad®. I’m going to assume you will be making the
same mistakes I did, so I’ll pass my thoughts on about the problems I had. When you’re
dealing with angles less than 10° changes are subtle and errors will not stand out. Be
absolutely sure that you are using the correct equation to work with the information that
you have available. All you need are two sides or a side and an angle other than 90°.
55
Figure 9
Rectangle, arc and tangent program
The first example I’m going to explain looks deceivingly simple and is typical of what
you have to start with, and believe me it isn’t easy, so pay attention. I started off this
drawing by putting a circle in a rectangle in no particular position on the X-axis and then
putting a 5° line against the tangent point of the circle. My next task was to figure out the
missing points with a calculator. The only practical way to accurately figure these points
out is with trig.
First we have to find and solve the missing values for the right triangles shown in Fig. 10
below. The key triangles are shown in solid black.
56
Figure 10
First, what two things do we have to solve this triangle? We have the hypotenuse because
it is the radius of the arc and the 5° angle. From our tables we see that the 0.0436 was
derived by multiplying the hypotenuse (0.5) times the sin 5°; and the 0.4981 was the
product of 0.5 x cos 5°. This will give us our end-of-arc position.
The 0.0476 has to be calculated to give us the final X-axis point of the angle. We can
easily calculate the 0.5436 because it is the sum of 0.500 and 0.0436. This gives us one
side of the triangle that we know is 5°; therefore the dimension needed is the sin 5° x
0.5436. Adding up these 3 dimensions we end up with the 2.2488 X-axis dimension. We
now have all the numbers we need to generate the code to produce this part.
Take one more look at the complete drawing before starting to write the program. The
main thing I want you to learn is how important it is to solve for the correct triangle to get
the answers you need, and the many times you have to solve more than a single triangle
to solve what may seem as a straightforward problem.
Figure 11
This program is just an exercise, and I’m not going to write any Z-axis code. The 0
starting point is located in the upper right-hand corner. Of course, we’ll also use cutter
comp to generate this shape. Now, read the code I wrote and examine Fig. 11 again and
visualize where the starting and stopping points are in your mind before you run the
program in backplot. This is what we are striving for, because a real professional
programmer can read code like a letter.
57
The entire program:
%
(rectangle, arc and tangent)
g00 g40 g90 x0 y1 z0
g41 d1 x0 y.5
g01 y0 f16
y-2.000
x-1.7032
g03 x-2.2013 y-2.4564 i0 j-.5
g01 x-2.2488 y-3.000
x-4.000
y0
x0
x.5
g00 g40 g90 x0 y1 z0
%
With comments
%
g00 g40 g90 x0 y1 z0
g41 d1 x0 y.5
g01 y0 f16
Last time, I started at y1 position so I could enter into the cutter comp mode in
two moves and coming in from the correct direction (remember—gear downtouch down).
y-2.000
x-1.7032
g03 x-2.2013 y-2.4564 i0 j-.5 –Last time, The x and y positions where the arc
ends.
g01 x-2.2488 y-3.000
x-4.000
y0
x0
x.5 –Exiting g41 mode in correct direction.
g00 g40 g90 x0 y1 z0
%
Work out a couple of similar problems on your own while I get ahead of my students
again. Boy, you guys are smarter than I thought you were.
The plot is about to thicken with your next problem that I called the pulley
program.
58
Figure 12
In this problem all we know is the radii of both circles and the distance between them, yet
we have to arrive at the tangent points.
Figure 13
Here is the real problem. The seemingly obvious way of solving this problem would be to
solve the angle that can be generated with the differences between the radii and the
distances between centers and then use this information to come up the needed points.
Wrong. Compare the two angles in Fig. 14. Although the error isn’t that great for laying
out sheet metal work, it’s a gigantic error for a computer to swallow, and you have to be
accurate to four places.
59
Figure 14
Believe me, I studied this problem for a long time before I was able to solve it. I also
came up with unusually simple way to arrive at the second side of the right triangle so the
problem was solvable. I don’t want to blow my own horn, but it is extremely rare that an
individual like myself, who hasn’t studied high math, will ever come up with a complex
mathematical rule on his own that works, whether mathematicians know about it or not.
Figure 15
Now we can calculate the angle because the sin B = hypotenuse ÷ side b. With this angle
we now know the remaining missing tangent points can be solved with your calculator.
Note that once we know that angle, it should be noted the same angle falls in two other
places as shown in Fig. 15 above. This allows us to solve the remainder of the problem in
Figure 16 in the same manner as we did in Fig. 15.
60
Figure 16
Let’s write the code for this simple yet not-so-simple shape. One thing I must state again
is that I’m having a terrible time with careless errors. I think the problem is that I’m more
worried about how I’m going to explain each problem than I am in entering the correct
numbers. Don’t fall into my trap. You don’t have to explain to me how you did it, so
learn from my mistakes. Become a hermit while you are studying so you don’t make
careless errors.
The entire program:
%
(pulley program)
g00 g40 g90 x0 y1 z0
x-.500
g41 d1 y.500
g01 y0 f12
g02 x-1.0625 y-.4961 i-.500 j0
g01 x-3.0313 y-.2480
g02 x-3.0313 y.2480 i.0313 j.2480
g01 x-1.0625 y.4961
g02 x-.500 y0 i.0625 j-.4961
g00 g40 x0
x0 y1 z0
%
61
I believe that you should be able to follow the pulley program without comments now
that you have calculated the tangent points.
Our next problem is linking to arcs together, and in this case the arcs are going in
opposite directions. What I want you to notice in this particular program is the fact that
you enter cutting the second 0.300 radius from the opposite direction as you did in the
same radius on the opposite side. This changes the i and j values going in and coming
out.
Figure 17
When you have to solve a problem like this, the first thing you have to do is determine
what you have to work with. In this case, we know the two radii of the arc and the width
of the straight section leading to it. Studying the drawing you will find that with the
information known there is only one position where we can begin to solve for the missing
dimensions to write our program.
The radii will give us the hypotenuse of the triangle we need to form, and we can
determine the second side of the triangle by adding together the radius of the first arc and
the distance the second arc’s center is from the edge. Now we can calculate not only the
starting point of the first arc (b=√c² – a² = 0.7437), but also the angle of that triangle (sin
A° = a ÷ c = 36.4837°). With the angle now known we can calculate the x, y ending
points of the arc, and we have already calculated the i and j values for that radius.
The ending point of our first arc is also the starting point of our second arc; therefore,
because the part is symmetrical, the ending point of the second arc is located the same
distance from the center point of that arc. To start the third arc new i and j values must be
determined, because we are approaching this arc from the opposite direction even though
this arc is identical to arc one.
62
Figure 18
Don’t just look at my answers and assume they are right. In the real world you don’t
solve problems you know the answers for. I’m writing this stuff for you to teach you how
to do it. I already know. Be original and change a few basic dimensions and see if you
can be confident that your answers are correct. That’s what it is all about. Don’t find out
that you don’t know how to do it by making bad parts. We are machinists who don’t have
erases to work with. Don’t become one of those “Oh shit” machinists who can only have
their mind work at full potential after they screwed up! Another free lecture by J. Martin.
Now let’s write the code for this beauty. Also, I added a couple of Z-axis movements that
might be used in the real world.
%
(rod-end)
g00 g40 g90 x0 y0 z0
g41 d1 x-.75 y-.25
g01 x-1 y-.25 f25
z-.5
x-2
g03 x-2.2412 y-.3716 i0 j-.3
g02 x-2.2412 y.3716 i-.5025 j.3716
g03 x-2 y.25 i.2412 j.1784
g01 x-1
x-.75
z0
g00 g40 x0 y0 z0
%
63
Figure 19
The rod program adds a useful new tool to our collection. The “r” letter designates
“radius” when it’s used in the same block as the circle command g02 or g03. This
simplifies code writing because it eliminates the need to calculate the “I” and “j” points
that are always changing as seen in our last example; however, the start and end points of
an arc must be calculated to the same degree of accuracy. I felt obligated to teach you the
hard way first because many older CNC systems don’t have the advantage of the r
command, and that’s the type of systems that many beginners will end up running. You
will see in the rod program just how much tedious code writing it eliminates.
(For this program you will need to add a new Tool #1 listed as .250" long and .125"
diameter.)
%
(Connecting rod)
g00 g90 g40 x0 y0 z0
g01 x-1 y.5
g41 d1 y.1
g01 y0 f15
g02 x-1.5638 y-.1858 r.3125
g03 x-1.6844 y-.125 r.15
g01 x-2.9406
g03 x-3.0612 y-.1858 r.15
g02 x-3.0612 y.1858 r-.3125
g03 x-2.9406 y.125 r.15
g01 x-1.6844
g03 x-1.5638 y.1858 r.15
64
g02 x-1 y0 r.3125
g01 y-.1
g00 g40 x-.5
x0 y0 z0
%
This concludes your basic course on CNC g-code programming. You’ll know if you
passed this course as soon as you attempt to write your own code to make a particular
part that you need. You now have the knowledge to produce a very complex part. The
next stage of codes to learn will only simplify the writing of the code you now know how
to write. I believe that working before you move on you should build up your confidence
by producing some parts that you can use before traveling on.
Machining Tip—Use multiple end mill holders as a quick way to change tools
Sherline 3/8" end mill holders P/N 3079 offer a quick and accurate way to change
tools. If just one tool holder is used, the cutter height must be adjusted each time it
is changed. If multiple holders are used, each with its own tool pre-adjusted to the
correct height, tools can be interchanged quickly with excellent repeatability on
their height setting. There is also a holder with a thread to accept a Jacobs 1/4" or
3/8" drill chuck, so they can also be interchanged like end mill holders. It is P/N
3074.
EMC Tip—Pausing a cut during a long program
If for some reason you have to stop your machine while it's running a long
program and you are planning to complete the part the next day, the safest way to
accomplish this is to stop the program by using [FEEDHOLD]. Turn the spindle
and servo driver off, but leave the computer on. The next day you can restart your
program by simply turning the drivers and spindle on and clicking on the
[CONTINUE] button. In this case the [FEEDHOLD] button becomes the
“Continue” button when it is used to stop the slide movement. If possible, try to
stop the operation at some point where the cutter is either not cutting or is cutting
in an area where finish doesn’t matter. It's also a good idea to write down the zero
positions of the handwheels and slides just in case you have to use the emergency
stop.
More handy g-codes
The g92 command
G92 resets your home position values. This command is used to reload the registers in
the control system with desired values and could be handy if you end up using a home
position that isn’t all zeros. Programming will always be simpler if you forget about some
of these neat features and always have home positions x0,y0,z0. No movement of the tool
along any of the axes will occur; it will simply reset the values in the axis readout
window to the home position values or whatever values you enter. This is used when, for
example, you shut down the computer at the end of the day with the machine in the home
position. When you turn it on the next time, the axis values may read all zeros or some
other numbers for x, y, z and a on the coordinate part of EMC screen instead of your
65
home position. By placing the home position values after the g92 it will reset your axis
readouts to the home position (no movement of tool along any of the axes will occur)
when you hit [Run] and begin the program.
Example:
%
g92 x1 y0 z2
g00 g90 g20 g40 z2 x1 y0 (home position)
g89 x2 y1 z0.50 r1.5 p.2 f5
g00 g80 x1 y0
%
g92 x1 y0 z2 – Would bring the coordinates on the axis screen in EMC from any number
that happens to be currently displayed to the (1, 0, 2) home position without moving any
axes (stepper motors) on the machine. Remember you must make sure your machine is
actually located in the home position to make this effective. It does not physically home
the machine, it simply resets the values to whatever coordinates you enter after the g92.
Canned cycles
There are quite a few canned cycles designed into the EMC program. They can save a lot
of repetitious programming. There are some others that EMC does not support or
Sherline machines cannot perform, so we’ll only consider the canned cycles that are
useable with Sherline CNC machines. These commands are primarily used for drilling
and boring cycles to save programming time when you have a lot of repetitious
operations to perform, like a series of holes. However, at this point you have learned
enough g-codes to be able to make most parts, and I believe you should take a break from
learning and take the time to become more proficient with the skills you have learned up
to now. Although these remaining commands are easier to learn than the ones you have
been using, I’d suggest you take a look at my last two programs at the end of this section
and read my closing comments before going on. Though you now know enough to make
parts without them, the following g-commands, when used appropriately, can eliminate
many lines of code from your programs and allow you to enjoy the full power of EMC.
The G80 command
The g80 command is used to cancel a canned cycle. It’s used in a similar fashion as the
g40 and g49 commands.
The g81 command
The g81 command is intended for drilling, and because x, y movements usually take
place with the drill located well above the part to avoid accidental collisions with
fixtures, the most efficient method is to lower the drill in rapid (g00) to the starting point.
However, the computer needs to know the drill starting point to accomplish this. This
second z-axis position is given by entering an r-command defining an absolute position in
the same line of code that contains the g-command that requires it. (Note that the rcommand is also used as a method of entering the radius when programming movements
that produce circular shapes; however, the EMC can tell the difference based on when it
is used.) If the depth of the hole exceeds 1.5 times the diameter of the drill you should use
the g83 command. Also note that we are using the absolute mode.
66
Example:
%
g90 g40 g20 g00 g80 z2
x0 y0
g81 x2 y1 z-0.50 r0.010 f3
g00 g80 x0 y0
%
(Consider the top of your part to be the 0 position.)
%
An explanation, line by line:
g90 g40 g20 g00 g80 z2 – It’s a good idea to get the z-axis up out of the way before
moving the x- or the y-axis. For example, consider what happens if you start the program
from a different position than you intended and the drill hits the fixture on the move to its
home position.
x0 y0
g81 x2 y1 z-0.50 r0.010 f3 – This line of code contains all the information to put the g81
canned cycle into effect, and you’ll be able to repeat it each time a new x, y position is
given.
g00 g80 x0 y0 – When you have completed drilling all your holes, a g80 is entered to
cancel the canned g-cycle command.
For drilling more than 1 hole, add the needed x, y positions for each hole; for
example:
%
g40 g20 g90 g00 g80 z2
x0 y0
g81 x2 y1 z-0.50 r0.010 f3
x3
x4
g00 g80 x0 y0
%
The g82 command
G82 is intended for drilling when you want a dwell at the bottom of the hole. (I find
this a bad idea when drilling, because some of the more exotic metals like stainless steel
may work harden and cause the drill to become dull sooner than it should.)
1. Move the z-axis only at the current feed rate to the z position.
2. Dwell for the given number of seconds. The length of the dwell is specified by
a p# designation in the g82 block and time entered would seldom be more than a
second.
3. Retract the z-axis at rapid rate to clear z. The motion of a g82 canned cycle
looks just like g81 with the addition of a dwell at the bottom of the z-axis move.
67
Example:
%
g90 g40 g20 g80 g00 z2
x0 y0
g82 x4 y5 z-0.50 r0.010 p0.2 f3
g00 g80 x0 y0
%
The new command to learn is command is p.
The g83 command
G83 is intended for deep drilling because you’ll break the drill if you don’t retract it
periodically. When you retract the drill it allows the chips to fly off and lets cutting fluid
wet the bit and the work before they gall or weld themselves to the drill bit. The general
rule when using a CNC machine is to have the drill cut no deeper than its diameter
without retracting it for the above reasons. This is called peck drilling.
The peck drilling cycle should also be used when center drills are used to create starting
points for your drills. Center drills twist off very easily because their drilling section is
not relieved as much as a drill is. This is done to force the drill to seek center; however,
they become very vulnerable to breakage. The z-axis should be retracted when center
drill’s depth has reached 60% of the needed depth. Note that drills will wander by a far
greater amount than you can imagine (especially if they are old and dull) if a center or
spotting drill isn’t used to develop a starting point. I prefer spotting drills (short drills
with a 90 degree point that cuts to center) over center drills because there is no small
point to twist off. They also have a proper chamfer angle and a faster machine operation.
This cycle takes a q value given as an increment value. This represents the increment of
movement along the z-axis before the drill is retracted to clear the chips. Again,
machinists refer to this as peck drilling.
1. Move the z-axis only at the current feed rate downward by delta or to the zposition, whichever is less deep.
2. Retract at traverse rate to clear z
3. Repeat steps above until the z-position is reached.
4. Retract the z-axis at traverse rate to clear z.
Example using a ¼" drill and putting 3-holes in 1.00" deep:
%
g00 g40 g20 g90 g80 z2
x0 y0
g83 x1 y1 z-1 r0.010 q.25 f2
x2
x3
g00 g80 x0 y0
%
The new command to learn is q.
68
The g84 command
G84 is intended for right-hand tapping. The Sherline CNC system doesn’t have any
provision to accomplish this.
The g85 command
G85 is intended for boring, which is a motion very similar to G81 except it adds feed
out. Usually you use a feed rate around 0.001" per revolution.
Therefore, 1000 RPM = 1-inch feed rate and so on. The reason you want to feed a boring
tool out is to eliminate a spiral tool mark that would result from a rapid retract; therefore,
the tool will feed out at the same rate as it was fed in. The tool will usually take a second
cut as it is withdrawn because a different cutting edge is cutting on the way out. For an
explanation of why you bore holes rather than drill them see the boring head instructions
at http://www.sherline.com/3054inst.htm.
Example:
%
g90 g40 g80 g00 g20 z2
x0 y0
g85 x2 y1 z-0.50 r0.010 f3
g00 g80 x0 y0
%
The g86, g87 and g88 commands
G86, g87 and g88 are intended for boring with starts or stops of the spindle, so these
are not used for the Sherline CNC system because Sherline machines do not have spindle
motor control.
The g89 command
G89 is intended for boring and uses a p value, where p specifies the number of seconds
to dwell at the end of the hole. The problem with dwelling at the bottom of a bored hole,
especially with a machine as light as a Sherline, is that tools have a tendency to chatter. I
usually don’t bore a hole to the exact bottom unless it is absolutely necessary. Remember
that in the Sherline general instructions, which I hope you have read, chatter is usually
cause by taking too heavy a cut, but it can also be caused by having a cut so light that the
tool skips around on the surface. Also consider the fact that chatter can damage the hole,
because as the chatter occurs at the bottom of the hole, the tool will usually remove
material from the sides and cause it to be oversize.
1. Move the z-axis only at the current feed rate to the z position
2. Dwell for given number of seconds p1 (1 second)
3. Retract the z-axis at the current feed rate to clear z. This cycle is like G82
except that the tool is drawn back at feed rate rather than rapid.
Example:
%
g90 g40 g80 g00 z2
x0 y0
g89 x1 y1 z-0.50 r0.010 p0.5 f3
69
g00 g80 x0 y0
%
For boring more than one hole, add the needed x, y positions for each hole.
The L and the g91 command
NOTE: Although I recommend using lower case letters in your programs because I
believe it makes the code easier to read, the letter l is a special case because it is easily
mistaken for the number one; therefore, I use the upper case letter L. (You might also
want to consider this for the letter Q.)
It’s time to learn about drilling a series of holes without writing any unnecessary lines of
code. The L command will allow you to drill or bore many holes on either the x- or yaxis with a single line of code, but it can be tricky to use at times. Unless this is
something your need to be doing I’d skip it for the time being.
The reason confusion can quickly develop is you have to be in g91 (incremental) in order
to implement this function and many things change. When you’re in g90 (absolute) the r
value is given as a point; however, in g91 you use the actual distance the r point is from
where you are located, and this will always be a negative number. The z programmed
distance in the canned cycle g-code is now given as the distance in incremental from the
r-point. This will also be a negative number and many times the number will be less of a
negative number than the r number as in the example below. Note that we are using the
g98 command in this series of examples.
Example using a ¼" drill and putting 3-holes in a row 1/4" deep:
%
g00 g20 g40 g80 g90 z0.50
x0.50 y0
g91 g81 g98 x1 y0 z-0.30 r-0.45 L3 f3
g00 g90 g80 x0.50 y0
%
Example using a ¼" drill and putting 12-holes ¼ " deep:
%
g00 g20 g40 g80 g90 z0.50
x0.50 y0
g91 g81 g98 x1 y0 z-0.30 r-0.45 L4 f3
x0 y1
x-1 y0 L3
x0 y1
x1 y0 L3
g00 g90 g80 x0.50 y0
%
An explanation of each line of code:
%
g00 g20 g40 g80 g90 z0.50
x0.50 y0 – Home position
g91 g81 g98 x1 y0 z-0.30 r-0.45 L4 f3 – First row with 4 holes, in increments of 1 along
the x-axis from (x1.5, y0, z0.50). Same motion as described in previous example, except
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for number of holes (number of repetitions L is set to L4). The g98 command is required
to have the z-axis at its original starting position, which is 0.500" above the part because
we are in incremental (g91).
x0 y1 – 1st hole in the second row, increments are x=0, y=1; therefore, the tool travels
from the last hole in the first row to the 1st hole in the second row for 1 along y-axis and
makes one hole (motion along z-axis is the same as described in previous example).
x-1 y0 L3 – Next 3 holes in the second row, increment for x=-1, y=0. Since L3 is number
of repetitions, 3 holes in increments of x-1 along the x-axis are going to be drilled
(motion along z-axis is the same as described in previous example).
x0 y1 – 1st hole in the third row, increments for x=0, y=1, tool travels from the last hole
in second row to the 1st hole in the third row for 1 along y-axis and makes one hole
(motion along z-axis is the same as described in the previous example).
x1 y0 L3 – Next 3 holes (L3) in the third row in increments of 1 along x-axis, increments
for x=1, y=0, (motion along z-axis is the same as described in the previous example).
g00 g90 g80 x0.50 y0 – Back to home position, g80, g90, cancel canned g-cycle and
incremental distance mode.
The g92 and g92.2 commands
Can you imagine how hard cnc programming would be if you had to write programs in
relation to the work’s position on the machine? It’s always easier to write code from a
convenient point in relation to the part rather than its actual position on the machine. This
is usually more of a problem on full-size machining centers that have built in homing
cycles than on a Sherline with its convenient “Zero All Axes” command. Many times
you may want to produce duplications of the same part in a single run. Without the g92
command each part would require separate programming.
The g92 is a handy command to eliminate these problems. It simply resets the axis
included in the same line of code to the number included with the axis designation which
is usually zero.
For example:
g92 x0 y0 resets your present position to x0 y0.
The next problem is canceling this command and getting back to the standard g90
coordinate system after that particular section of code has been run. The rules to do this
are a little more specific: You must be in exactly the same position when you cancel this
command with a g92.2 as you were when you entered it; therefore, this is what a full
block of code would look like that might be inserted into some program starting at the
g92 command:
g92 x0 y0
g00 x0.500
z-0.500
g01 z-0.750 f3
x1.500
y1.000
x0.500
y0
z0
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x0 y0
g92.2
This leaves you exactly back where you started and back under the g90 command. To
eliminate confusion it’s also important to note that the EMC position display also resets
to whatever is called for when the g92 command is given.
The g98 and g99 commands
These commands are needed when you are under the g91 command (incremental) to
control the retracted z-axis position when drilling a series of holes using the L
command. It’s also another method of bringing confusion into your life.
The g99 command
G99 avoids retracting a drill all the way up to the original z-position between moves, thus
saving valuable time on a project that involves hundreds of holes.
Example using a ¼" dia. drill and putting 8 holes ¼ " deep:
%
g00 g20 g40 g90 g80 z0.50
g91 g81 g99 x0 y0 z-0.30 r-0.45 f4
x1.5 y0 r0
x1 y0 L2
x0 y1
x-1 y0 L3
g98
g00 g90 g80 z0.50
x0 y0
%
This program looks pretty much the same as the program that uses g98; however, there’s
a significant difference. Note the added r0 in line 4. The reason it’s needed is to cancel
out the r-0.45 in line 3. Remember, when we implemented the g99 command the z-axis
was located 0.45" above the position where the z-axis is now located. If you didn’t enter
the r0 the z-axis would rapid down one more time for 0.45" and break the drill. The x-1
in line 7 is to over-ride the x1 in line 5 that will control the direction on the x-axis the
holes are drilled in. Enter this program into EMC and run it without the drivers turned on
to watch the results, and you’ll realize why a complete understanding of these new
commands is necessary to avoid a lot of tool breakage and ruined parts.
Last, but not least, I’ll write the program that we have just completed in the code that we
knew before learning about canned cycles.
%
g00 g20 g40 g90 z0.50
x0 y0
z0.050
g01 z-0.250 f3
g00 z0.050
x1.500
g01 z-0.250
g00 z0.050
72
x2.500
g01 z-0.250
g00 z0.050
x3.500
g01 z-0.250
g00 z0.050
y1
g01 z-0.250
g00 z0.050
x2.500
g01 z-0.250
g00 z0.050
x1.500
g01 z-0.250
g00 z0.050
x.500
g01 z-0.250
g00 z0.050
z0.500
x0 y0
%
Now consider how much programming labor these canned cycles can save once you learn
them. Twenty-eight lines of code was reduced to nine lines; however, I spent far more
time just learning why you have to put the r0 in programs using the g99 command than I
did writing the above program, especially when you can just use the [Copy] and [Paste]
commands.
th
Using the optional 4 axis
The Sherline driver board was designed to accommodate the fourth (A) axis; therefore,
all that is needed is P/N 8730 rotary table that includes both the proper stepper motor and
the stepper motor mount. It sells for $395.00 (2/05). The A-axis is programmed in
degrees. A minus entry will rotate the table in a counter-clockwise direction. The A-axis
can move in unison with the X-, Y- and Z-axes. Use slow feed rates to avoid a situation
where the A-axis cannot keep up because of the 72 to 1 worm ratio of the rotary table.
There isn’t any EMC software available at this time to write the complex code associated
with engraving or machining on a round surface; however, I believe the type of parts that
will be made by Sherline machinist are straightforward and can be easily programmed.
Engrave parts such as jewelry will need special programs. I’m sure I’ll be writing more
on this subject when I find out just what type of work you want to run with this device.
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The Sherline 8730 CNC Rotary Table with stepper motor can be plugged directly into
the A-Axis cord pre-wired into your computer to operate as a 4th axis.
Conclusion
You’re ready to take off on your own
The next stop on the EMC highway is to visit Linux-CNC. The road to this town requires
a hookup to the internet to travel on. If you’re not connected to the internet you’re
missing one of the great advancements of civilization. It’s like having all the great
libraries of the world on your personal bookshelf. I have taught you the basic language of
g-code programming, and much more is available on the http://www.linuxCNC.org/ site.
A couple of members from this group have written some programs for simplifying codewriting that I’m sure you’ll find interesting. They have a users group that can be of great
help in solving code writing problems.
If you’re like me you will find a lot of satisfaction with this new ability to write a
program and then watch your faithful robot make parts for you at the push of a button.
Though the parts you make initially on this machine may be small, what you have learned
is not. When you master this, you will have gained the ability to make parts in shapes and
in numbers that cannot be matched by the world’s best machinists working by hand. If
you want, you can apply what you have learned to larger machines and larger parts later
on. Whether you took on this challenge just for the fun of it or as a way to solve an
immediate practical need for small precision parts, you are on your way to joining the
leading edge of today’s modern machinists.
If you found my instructions useful and you are not reading them to operate a Sherline
machine may I suggest a way to show your appreciation and help a good cause would be
to donate a few dollars to my foundation that is dedicated to getting great craftsmen the
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respect they deserve in this world. Check out http://sherline.com/jmfound.htm and be
sure to visit the Joe Martin Foundation’s Internet Craftsmanship Museum at
http://www.craftsmanshipmuseum.com/ where the marvelous work of these great
craftsmen can be viewed and enjoyed 24 hours a day.
Definitions and Codes
The word definitions listed below were copied from the Linux CNC website. It’s where I
gathered the information to write part two of these instructions. It’s worth reading and
using to go to the next step in programming, but for the time being stick with just my
instructions. I never intended to write a complete programming manual and was only
interested in writing enough instructions to get you up and running in the marvelous
world that we call CNC.
http://linuxCNC.org/handbook/gcode/g-code.html
I have highlighted in red bold face the main words we’ll be working with when using a
Sherline machine, and, although many of these words we will not directly use, I wanted you
to be aware of the codes used in industry. A CNC program “word” is defined as an
acceptable letter followed by a real value.
Table 1
Words acceptable to the EMC interpreter
D
F
G
H
I
J
K
L
tool radius compensation number
feedrate
general function (see below)
tool length offset
X-axis offset for arcs
X offset in G87 canned cycle
Y-axis offset for arcs and Y offset in
G87 canned cycle
K Z-axis offset for arcs and Z offset
in G87 canned cycle
L number of repetitions in canned
cycles and key used with G10
M
N
P
Q
R
S
T
X
Y
Z
miscellaneous function (see below)
line number
dwell time with G4 and canned
cycles
key used with G10 Q feed increment
in G83 canned cycle
R arc radius, canned cycle plane
S spindle speed
T tool selection
X-axis of machine
Y-axis of machine
Z-axis of machine
Miscellaneous words
M words are used to control many of the I/O functions of a machine. M words can start
the spindle and turn on mist or flood coolant. M words also signal the end of a program
or a stop within a program.
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Table 2—M Word List
M8 flood coolant on
M9 mist and flood coolant off
M26 enable automatic b-axis clamping
M27 disable automatic b-axis clamping
M30 program end, pallet shuttle, and reset
M48 enable speed and feed overrides
M49 disable speed and feed overrides
M60 pallet shuttle and program stop
M0 program stop
M1 optional program stop
M2 program end
M3 turn spindle clockwise
M4 turn spindle counterclockwise
M5 stop spindle turning
M6 tool change
M7 mist coolant on
Preparatory Words
Some g words alter the state of the machine so that it changes from cutting straight lines
to cutting arcs. Other g words cause the interpretation of numbers as millimeters rather
than inches. While still others set or remove tool length or diameter offsets. Most of the g
words tend to be related to motion or sets of motions. Table 3 lists the currently available
g words.
Table 3—G-code List
g0 rapid positioning
g1 linear interpolation
g2 circular/helical interpolation
(clockwise)
g3 circular/helical interpolation
(counterclockwise)
g4 dwell
g10 coordinate system origin setting
g17 xy plane selection
g18 xz plane selection
g19 yz plane selection
g20 inch system selection
g21 millimeter system selection
g40 cancel cutter diameter compensation
g41 start cutter diameter comp. left
g42 start cutter diameter comp. right
g43 tool length offset (plus)
g49 cancel tool length offset
g53 motion in machine coordinate system
g54 use preset work coordinate system 1
g55 use preset work coordinate system 2
g56 use preset work coordinate system 3
g57 use preset work coordinate system 4
g58 use preset work coordinate system 5
g59 use preset work coordinate system 6
g59.1 use preset work coordinate system 7
g59.2 use preset work coordinate system 8
g59.3 use preset work coordinate system 9
g80 cancel motion mode (includes canned)
g81 drilling canned cycle
g82 drilling with dwell canned cycle
g83 chip-breaking drilling canned cycle
g84 right hand tapping canned cycle
g85 boring, no dwell, feed out canned cycle
g86 boring, spindle stop, rapid out canned
g87 back boring canned cycle
g88 boring, spindle stop, manual out canned
g89 boring, dwell, feed out canned cycle
g90 absolute distance mode
g91 incremental distance mode
g92 offset coordinate systems
g92.2 cancel offset coordinate systems
g93 inverse time feed mode
g94 feed per minute mode
g98 initial level return in canned cycles
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Table 4—G- and M-Code Modal Groups
Group 1 = {g0, g1, g2, g3, g80, g81, g82, g83, g84, g85, g86, g87, g88, g89} —motion
Group 2 = {g17, g18, g19} — plane selection
Group 3 = {g90, g91} - distance mode
Group 5 = {g93, g94} - spindle speed mode
Group 6 = {g20, g21} - units
Group 7 = {g40, g41, g42} - cutter diameter compensation
Group 8 = {g43, g49} - tool length offset
Group 10 = {g98, g99} - return mode in canned cycles
Group12 = {g54, g55, g56, g57, g58, g59, g59.1, g59.2, g59.3} coordinate system selection
Group 2 = {m26, m27} - axis clamping
Group 4 = {m0, m1, m2, m30, m60} - stopping
Group 6 = {m6} - tool change
Group 7 = {m3, m4, m5} - spindle turning
Group 8 = {m7, m8, m9} - coolant
Group 9 = {m48, m49} - feed and speed override bypass
There is some question about the reasons why some codes are included in the modal
group that surrounds them. But most of the modal groupings make sense in that only one
state can be active at a time. Note: It isn’t necessary to try to remember the words I
highlighted. You’ll learn these as we go.
NOTE: I have purposely started using lower case letters to designate cnc because I
would like to encourage its use as simply a word rather than an abbreviation for
Computer Numeric Control. This is the future of machining--simply the way things will
be done--and the designation cnc will become so common eventually as to be just the
word people use to describe having a machine driven by a computer make a part for you.
–Joe Martin
Frequently Asked Questions
Following is a list of questions answered in this section:
• I'm not an experienced machinist. How do I learn more about cutting
metal?
• How hard is it to hook up the computer?
• I already have a computer. Can I use mine and save some money?
• I already have a Sherline mill. Can I buy the rest of the components and
retrofit my mill?
• I live someplace other than the United States and our current is 230 volts,
can I still use my cnc system here?
• What format are the instructions in?
• Where can I find a current copy of all of the instructions on the Sherline
Documentation CD?
77
• What is Linux?
• What is EMC?
• What programming language does the EMC system use?
• What other programs are included on the CD that comes with my system?
• What do I do if I don’t know how to use Linux or cnc?
• I’m ready to start writing the G-code to make my part. How do I get
started?
• How do I run a CAD file on my cnc system?
• How do I transfer my G-code files to my cnc computer from my CAD /
CAM computer?
• Will G-code created by any given CAD/CAM software run perfectly the
first time on EMC?
• What is a "feedback loop" and do I need one?
• How fast will the stepper motors move the slides?
• How do I use my inch cnc system in metric mode?
• My stepper motors make noise, but nothing is moving. What should I do?
• What is the difference between "Unipolar" and "Bipolar" stepper motors?
• I have read the entire Sherline Documentation set front to back, now what
to I do?
• For some reason my axes are going in the wrong direction when I Jog.
What am I doing wrong?
• Why does my computer lock up after running a small program a number of
times?
• Does Sherline use the latest version of EMC?
• I want to connect a USB device to my Sherline computer. How do I set it
up?
• Other than calling Sherline, where are some other places I can go to get
help on my specific questions on machining, cnc and using Sherline tools?
• What is GPL and what does it mean to me?
• Is there a way to convert a photo to g-code?
• Can I mill threads without a cnc rotary table?
• What if I have a question that isn't answered here?
How hard is it to hook up the computer?
Sherline has made everything as easy as possible for you. The computer has the operating
system and software pre-installed. The driver and power supply are also pre-installed
inside the computer box. All you have to do is plug in some cords to get up and running.
There are some good pictures in the printed step-by-step "Quickstart" guide that comes
with your system. They show you how to plug in your new Sherline cnc computer and
stepper motors. (Don't forget to plug in the parallel cable...) In addition to the printed
sheet, it is on the Sherline Documentation CD that comes with the system where it is
called quickstart.htm. Here you can see photos of the system and the back of the
computer to see exactly how to plug everything in. If you aren’t familiar with computers,
please be sure to pay attention, as you can damage the system if you force things into the
wrong plugs.
78
I already have a computer. Can I use mine and save some money?
You can, but you might want to consider your options before you decide. Basically you
have two ways to go:
1) Buy a new cnc-ready Sherline machine or retrofit your existing mill, add stepper
motors (P/N 67127, $75.00 each), buy a driver box to power the stepper motors
(Sherline's is P/N 8760) and plug that into the parallel (printer) port on your computer.
Then you have the choice of loading Linux and EMC (which comes on CD with the
driver box) or running the Sherline system or using a Windows® or DOS based software
that you purchase elsewhere. If you are not familiar with Linux, doing the installation
yourself could cause you some problems; particularly if all the components of your
system are not compatible with Linux, but the new Debian version of Linux is much
more user friendly than the earlier Redhat version so it will probably go smoothly. We
just can't guarantee it, which is why we offer the system complete with the computer.
Purchase of the driver box does NOT include free software support. If you purchase
software from another source, make sure it will run with the Sherline driver box. They
may want you to purchase a driver box and stepper motors from them. (For more
information about implications of installing and using Linux compared to other operating
systems, CLICK HERE.)
or
2) Buy the complete Sherline system with a new computer, connect the cords, boot it up
and start working right away. When we designed our system we initially planned to let
customers do the Linux/EMC installation on their own computer to keep the cost down.
When we found out how many variables could effect the installation we decided it would
be worth it to include new computer with the OS and software already loaded and tested.
That way we avoid having to answer all those phone calls from frustrated users trying to
get their system to work. If you are not absolutely sure you are up to the task of
installing Linux yourself we highly recommend that you purchase the complete
system including the computer.
I already have a Sherline mill. Can I buy the rest of the components and retrofit my
mill?
Yes. We now offer systems that include a retrofit kit for either a 5400 or 2000-series mill,
three stepper motors and the computer with drivers and software from the full system.
Basically it’s the complete system less the mill. For a 5400-series mill the part number is
8542 (inch) or 8543 (metric). For the 2000-series mill the part number is 8022 (inch) or
8023 (metric). Price for either system is $1775.00. Retrofit kits are also available for
Sherline lathes. See www.sherline.com/CNCprices.htm.
I live someplace other than the United States and our current is 220 volts, can I still
use my CNC system here?
Yes, but you will need to toggle two switches for this to happen. The back of the
computer’s power supply has a red switch for switching between 110/115 and 220/230
79
volts. You will need to flip this switch to 230. You can easily switch it with a small
screwdriver or any other small flat device. Secondly, you will need to switch the driver
board’s power supply so that it will be set to use 230 volt power. There is a switch that is
basically identical to the one on the back of the computer. You will need to open up the
computer’s side panel by unscrewing the two screws on the back. The side you will be
unscrewing is the one with the power switch for the driver board. MAKE SURE that all
power is unplugged, as even if the computer is off it will still have live power to the
driver board. Once you have removed the side panel you will need to flip the switch in
the middle of the power supply on the side facing you. It is somewhat embedded into the
side, so you might need to get a screwdriver instead of just using your fingernail like you
might be able to do with the switch on the back of the computer. Be sure that you have
the right setting for the power in your area, as having it switch wrong it will cause
damage to the system.
If you are using the 8760 driver box to drive your stepper motors, the separate power
supply included with that box will accept any incoming current from 100 VAC to 240
VAC and automatically provide the correct DC output current to the drivers. It comes
with a USA type 3-prong grounded plug, so a different cord or a wall plug adapter will be
required in countries that use other configurations.
What format are the instructions in?
All of the instructions are available in HTML format [.html]. This format is readable on
just about any operating system without any troubles. Many of the files are also formatted
in Adobe Acrobat [.pdf] and Microsoft Word [.doc] formats. It should be noted that PDF
and Word files may not be readable on your system depending on the software you have
installed. You will be able to open the HTML file in your favorite web browser, and .pdf
files can be opened on Linux computers supplied by Sherline. The Adobe Acrobat Reader
program required to open .pdf documents on Windows computers is available for free
download at www.adobe.com if you do not already have it.
Where can I find the most current version of all of the instructions on the Sherline
Documentation CD?
The most up-to-date 4.xx version of the instructions can be found at
www.sherline.com/CNCinst4.htm. For those using a system purchased before January 1,
2005, instructions for the 2.xx Redhat version can be found at
www.sherline.com/CNCinst.htm.
What is Linux?
Linux is an operating system. An operating system is the basic set of programs and
utilities that make your computer run. Some other common operating systems are UNIX
(and its variants BSD, AIX, Solaris, HPUX, and others); DOS; Microsoft Windows;
Amiga; and Mac OS.
80
What is EMC?
EMC is the Enhanced Machine Controller originally developed by National Institute of
Standards and Technology (NIST). It is released under the General Public License (GPL).
Currently NIST does very little work on the project, and it has been taken over by
average Linux users and a handful of very talented coders. You can get up to date on the
project and get more detail on the movement of it by visiting its website at
http://www.linuxcnc.org
What programming language does the EMC system use?
The Sherline cnc system and EMC uses G-code. G-code is the standard language used to
program most CNC machines in industry and is probably supported by your favorite
CAD/CAM program. For simple shapes you can write the needed G-code yourself. For
complicated shapes you can draw your part in a CAD program and export it to G-code
which can then be used in EMC. (Exporting to G-code may require a second translator
program if your CAD program can’t do it.) More can be read about G-code and its uses in
the CNCinst.htm file included on the Sherline Documentation CD-ROM.
What other programs are included on the CDs that comes with my system?
We have included a number of free utilities that will help you create g-code. They are
located in the “Utilities” folder that can be found on one of the CD’s included with your
machine or driver box. They are all programs that run on your Windows® computer, and
the g-code files you generate can be saved in .txt or .ngc format and transferred to your
Linux computer to be run. They can also be found on the Sherline web site at
www.sherline.com/CNClinks.htm. The Linux/EMC installation disk also includes a
number of free Linux programs for word processing, spreadsheets, etc. A CAD/CAM
program called Synergy is also included. A limited version can be tried for free that
includes the CAD portion, but a key must be purchased from the developer in order to
use all the features.
What do I do if I don’t know how to use Linux or CNC?
There are a couple of options here. You can click on the icon for the instructions on your
EMC desktop. The same set of instructions is also on the Sherline Documentation CD.
You can get to it by putting the CD into your CD-ROM drive and opening the index.html
file located in the getting-started directory on the CD. You also might want to take a look
at the official Sherline Instructions; they are located both on your desktop, and on the
Sherline Documentation CD. The file is called CNCinst4.htm. There is also a large
amount of documentation on the internet. If our documentation doesn’t provide the
answer you seek, try your favorite search engine and search for your specific
problem/question, chances are somebody else has had the same problem. There are also
several user groups you can join that will most likely help you with support. While these
are not Sherline specific groups, they will most likely be familiar with the system you are
using, and if not something very close to it. A Sherline cnc owner's group of over 1000
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members can be found at www.yahoogroups.com by typing "sherlinecnc" in the query
box. Be sure to research your question before posting to these lists. Some list members
get frustrated when people ask questions before doing a bit of research first. You can
learn more about these mailing lists here: http://www.linuxcnc.org/links.html. When all
else fails Ray Henry is available for technical support for a reasonable by-the-hour fee.
He can be reached at rehenry@up.net and 906-875-6692.
I’m ready to start writing the G-code to make my part. How do I get started?
If you are new to the cnc community, it is suggested that you read the Sherline cnc
instructions all the way through before attempting to make parts. It is a great way for
those who aren’t familiar with cnc or G-code to get started in coding. By the time you are
finished reading the instructions you should be able to write simple programs and at the
very least understand other, more complicated instructions.
How do I run a CAD drawing on my CNC system?
You can’t run a CAD (Computer Aided Drafting) file directly in EMC or in most cnc
control programs. You first need to get the vector information in the CAD program
translated into the language of G-code, which is a text file consisting of just letters and
numbers. This is what the EMC program uses to talk to the stepper motors that move the
machine. With complete CAD/CAM programs like MasterCam®, SurfCam® or
GibbsCam® you can do a drawing and then output G-code, but these professional level
programs can be quite expensive. If you already have a CAD program and need to get
files into G-code, there are several free or very inexpensive “translator” programs
available that can do this for you. We include links to a few at
www.sherline.com/CNClinks.htm. To turn a CAD drawing into G-code you would open
one of these programs on your Windows® machine. Then you would open the .dxf or .stl
drawing file in that program and save it as a G-code file. The resulting text file can then
be opened in any program that can read .txt files, such as Wordpad®, WordPerfect® or
Microsoft Word® in Windows or by DOS and Linux programs. In EMC you would save
the file to your “gcode” folder (see below) where it can be opened and run. Keep in mind
that EMC uses very simple G-code, and the code written by a high end CAD/CAM or
translator program may need some lines removed or modified before it will run properly.
You can edit the G-code from within EMC and watch it run in the “Backplot” program
before turning on the stepper motors to actually make a part.
How do I transfer my G-code files to my CNC computer from my CAD/CAM
computer and vice versa?
There are a few ways you can do this, but the easiest way is to save your g-code as text
files on a floppy disk or write them to a CD on your CAD computer, then take the floppy
disk or CD and put it into your Linux computer (Note: The file needs to be saved with a
name consisting of eight characters or less in order to be able to transfer the file to the
EMC program). On the desktop there will be an icon that says “Floppy.” Left click on it
to open a browser window for the floppy drive. Simply drag and drop the file onto the
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desktop or into your G-code programs folder which is called “gcode.” When you are in
the EMC, you can open this file by browsing to it. To save a file to the floppy from your
computer, just drag the file from the “gcode” folder to the floppy window. Close the
browser window for the floppy by clicking on the “X” in the upper right corner of the
window. To save the file you will have to right click on the floppy icon on the desktop
and use the “unmount” command. This completes the file saving process. Do not remove
the floppy from the computer until the light on the drive goes out after unmounting.
What is a "feedback loop" and do I need one?
Most systems that use stepper motors do not have any type of "feedback" arrangement
that uses an encoder to report movement/position information back to the processor. A
true feedback loop using servo motors with encoders can compare specified movement to
actual movement and compensate for any skipped steps. It can also allow you to reverse
engineer existing parts by using a probe to touch points on its surface and create a
drawing of the part. In general, servo motors are more expensive than stepper motors.
Stepper motor systems rely on the fact that if you put power into stepper motor it will
accurately rotate a certain amount that happens to be 1.8° per step. By making the
electronics more complex you can micro-step a stepper motor and have it turn only 0.9°
or 400 steps for each revolution of the leadscrew. (This is what Sherline does.) By sizing
the motor appropriately for the mechanics of the machine you can make a safe
assumption that the motor will always have enough power to make the desired move
without stalling. Specifying a proper feed rate (see next question) will also help assure
that your machine does not "skip steps," making a feedback loop unnecessary. Sherline
feels a stepper motor system gives you the "most bang for the buck."
How fast will the stepper motors move the slides?
A fact when dealing with stepper motors is that the faster they turn, the less torque they
have. This is because the power for each pulse is on for shorter periods of time; therefore,
it's a good idea to keep feed rates 20% below maximum when running programs with
many short moves, particularly on the Z-axis. The maximum feed rate in EMC is 22
in/min. Therefore it is good practice to keep your feed rate below about 18 in/min or 450
mm/min. Some of our customers have counter-balanced the weight of the Z-axis with a
simple rope-pulley-weight device to reduce wear on the Z-axis leadscrew. See the
http://sherline.com/CNCproj.htm section of our website for a photo and description of
how one person did this. You'll find that the stepper motor system we use quite reliable
and capable of running complex programs without losing steps when used properly.
G-code tips: Start and end each program with a percentage sign. Put a g40, g49, g21
(Metric) or g20 (inch) and g90 in the first line of code to cancel out any previous codes
that might be left over from the last program, and always end the program by returning to
the same place you started. Keep in mind which g-codes EMC does and does not support.
Some canned cycles are not supported, for example.
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How do I use my inch CNC system in metric mode?
You can toggle between metric and inch modes by using a g20 or g21 code. A line of
code beginning with "g21" tells the machine that all numbers you enter after the g21 are
now in millimeters instead of inches. The software will make the calculation to move the
machine the correct metric distance using the inch leadscrew. Using the g20 code will
allow you to switch back to inch dimensions or to enter inch dimensions on a machine
with a metric leadscrew. So if you have an inch machine and always program in inches,
why should you worry about it? Because EMC remembers the last code run even when
the machine is turned off. Therefore, it is a good idea to always put in a g20 in the first
line of your inch program just in case the last program run had a g21 in it. On metric
machines start with a g21 to similarly protect yourself from a g20 code in the previous
program.
When starting the EMC program, select the proper file for your machine; that is, on an
inch machine, click on the desktop icon that says "Sherline Inch" or for a machine with
metric leadscrews, select the icon called "Sherline MM." This tells the program what
leadscrew pitch to assume in its travel calculations.
My stepper motors make noise, but nothing is moving. What should I do?
The likely problem here is your mill is binding or not properly lubricated. With the more
significant stress of quick back and forth motions and the high number of turns possible
in a short period of time your mill will need to be more frequently lubricated than hand
driven applications. Under continuous cnc use we recommend that Sherline cnc mills be
lubricated once every four hours. Refer to the mill manual or
http://www.sherline.com/lubricat.htm for more detailed lubrication instructions. Note
also that when stepper motors are powered up but not yet running they do tend to make a
slight buzzing or hissing noise. This is normal.
Why does my computer lock up after running a small program a number of times?
If you have a version of EMC earlier than 4.37 the problem may be due to a buildup of
CPU usage caused by running the same program over and over. (CPU usage is shown in
a small window near the bottom right of your screen.) Rebooting each time will work but
is time consuming. Ray Henry suggests your best solution is to turn off the Backplot
program when running short programs repeatedly. Another work-around is to copy and
paste a number of copies of the small program into one longer program. Put a M0
command between each copy of the program to pause the machine. When you replace
your part, just hit the [Resume] button to continue. This issue has been resolved in
versions of EMC from 4.37 on.
I have read the entire Sherline Documentation set front to back, now what to I do?
Well, our aim was to just start you on your path of learning Linux and cnc. There is a
whole lot you can learn beyond these instructions. For starters you can check out the
EMC website http://www.linuxcnc.org and get on the mailing lists. There are also more
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complex books and documentation on G-code available at your favorite book store or
library.
For some reason my axes are going in the wrong direction when I Jog. What am I
doing wrong?
This means that your ini file is improperly set. To fix it you will need to open the file
called mill_inch_freq.ini for machines with inch leadscrews or mill_mm_freq.ini for
machines with metric leadscrews. The files are located at /usr/local/emc. To get there,
you click on: K-Menu > Quick Browser > Root Folder > usr > local > emc. To open the
.ini file, just single click on it. You will need to change INPUT_SCALE and
OUTPUT_SCALE values from +1600 or -1600 to the opposite value; i.e., if yours is
+1600 and it is jogging backwards, change it to -1600 and vise versa.
I’m getting an error message that reads “Radius to end of arc differs from radius to
start..” What does that mean?
This means the endpoint of the previous line does not match the coordinates specified and
required by the radius command. The tolerance for the precision of these two points can
be adjusted in the INI files of version 4.51 or higher.
Making Tolerance Changes to EMC
Computers can be maddening devices because they demand accuracy beyond what
normal human beings find useful. This can be especially true when producing cnc
programs, and where this condition shows up the most is when you are working with
radius ending points.
In order to cut a curve, the g02, g03, and r commands must be used. When you use these
commands, you must tell your computer the exact ending position of the curve. The
computer will give you a message stating that your end x y position is in error but it will
not fix it for you. The computer is demanding an accuracy far greater than the user
believes the part needs and who may have carelessly made a few rounding errors.
Because Sherline cnc customers have been having problems with this, we decided in
11/06 to open up this tolerance up to a maximum error of 0.001" (0.002 mm) standard.
If you are still constantly having this kind of problem, you can either increase the
accuracy of your drawing or force the computer to accept your faulty math by opening up
the tolerance in the INI files although Sherline doesn't recommend it, believing two
wrongs don't equal one right. The radius point tolerance can be altered in EMC v4.51 and
higher in the INI files. Altering the INI files of previous versions will not fix the problem;
however, the EMC can be upgraded online without the need for reinstallation of the
software.*
To change the tolerance for radius and tangent points, simply edit the numerical values in
the INI files (mill_inch_freq.ini and mill_mm_freq.ini). The lines should be by default:
INCH_TOLERANCE = 0.0005 or 0.0010 (SP setting)
MM_TOLERANCE = 0.001
or 0.002 (SP setting)
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Changing the Axis Scale
Changing the axis scale (for leadscrews with a thread count other than 20 TPI or 1 mm
for example) can be achieved by editing the input and output scale values in the EMC ini
files (mill_inch_freq.ini or mill_mm_freq.ini for the Standard and Metric versions of
the EMC, respectively). To open these files, go to K-menu > Quick Browser > Root
Folder > usr > local > emc > Open In File Manager, which will open the directory
containing the EMC files, and then click on the file you wish to edit.
About a quarter of the way into the file you will see the section labeled "; Axes sections ------------" where the settings for all four axes are located. For each axis you wish to
change the scale on, go down to the lines that read "INPUT_SCALE =" and "OUTPUT
SCALE =". These values are normally 16000 (or -16000) in the Inch ini file and 800 (or 800) in the Metric ini file. Changing these values will affect how far the axes travel for
every unit jogged. For example, dividing the values by ten, would cause an axis to move
.1" when jogged by 1". So, when a machine is switched from a standard 20-TPI
leadscrew to a 4-TPI leadscrew, for instance, changing the scale values from 16000 to
3200 would compensate for this and return the machine to a normal movement scale.
When changing these values, make sure to leave the number either positive or negative,
as changing this will reverse the direction the axis moves unless this is what you want to
do.
There are a number of other values in the ini files that can be altered to change the way
the EMC functions, although experimenting with these may have effects ranging from the
EMC functioning properly to your program becoming impaired or inoperable. When
you're finished making whatever changes you like, simply save the file and restart the
EMC if it's currently open. A reboot should not be necessary, but is a good practice to
make sure the changes take effect. Should you ever need original copies of the ini files,
replacements (and their instructions) can be downloaded at the EMC section of the
Sherline website at http://www.sherline.com/emc/ini.html.
*Sherline Linux computers of version 4.xx are configured for connection to the Internet.
Once connected to the Internet with the proper network cable, open a terminal (second to
right icon on the taskbar) and type:
sudo apt-get update
Hit [Enter] key to start download, then type:
sudo apt-get install emc emc-modules-2.6.16-rtai
Hit [Enter] to install download
Does Sherline use the latest version of EMC?
Not necessarily, and here's why. Sherline uses the latest version of EMC that we have
tested and are sure is working properly. From time to time small bugs are fixed or more
features are added by people in the Linux group, and a newer version of EMC may
become available on another web site, but we will not use it until we are sure that the
other "fixes" that are inevitably incorporated into the new version don't cause other
unforeseen problems. The version of EMC that we install on our computers, offer for sale
on CD or make available on our web site for download is the latest tested, stable version
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that is supported by our instructions. If you choose to download a later version, you do so
at your own risk. The newer version may fix a fault that we did not consider a problem
when using it on a Sherline machine, and other fixes may cause previously unknown
malfunctions. If you have problems with any version of EMC newer than the one we
currently support, please do not call Sherline for technical assistance.
I want to connect a USB device to my Sherline computer. How do I configure
Linux?
Transferring programs from a Windows® computer can be done on a floppy disk or a
CD, but flash memory devices and cards are also an easy way to transfer data using the
USB port. Here's how to configure your Linux computer to accept them:
Installing a USB flash memory device in Linux:
· Boot up to the Linux desktop.
· Go to root directory.
(NOTE: Type carefully; changes made incorrectly can cause severe damage that will
require a complete reinstallation to fix!)
· To open the root directory, go to the lower left-hand corner of the Linux desktop and
click on the K-icon. (It is where the “Start” menu would be in Windows.) Select Logout >
End session only > OK.
· In the appropriate boxes type the words (shown in bold)—username: root, password:
sherline
· Run the Terminal Program (in the K menu, the icon looks like a little LCD monitor)
· Under sherline@localhost:~$ type the following commands (shown in bold):
mkdir /media/flash and press [Enter] (Note the space between mkdir and /media)
In the next line under sherline@localhost:~$ type the following command (shown in
bold):
mc and press [Enter] twice (to enter the Midnight Commander)
· Select and highlight the /etc directory and press [Enter]
· Scroll down and highlight the file called modules
· Press [F4] to edit the file. In the next empty line add the following text:
usb-storage and press [Enter]
· Press [F10] to save and exit > Select [Yes]
· Scroll up to find and highlight the file fstab
· Press [F4] to edit the file. In the next empty line add the following text:
/dev/sda1 /media/flash msdos,vfat noauto,users 0 0 (0 0 = zero zero) and press
[Enter], (Note the space between: sda1 and /media, flash and msdos, vfat and noauto,
users and 0, 0 and 0)
· Press [F10] to save and exit > Select [Yes]
· Press [F10] to exit Midnight Commander > Select [Yes]
· Under sherline@localhost:~$ type the following command:
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exit and press [Enter] (this command will end the Terminal Program.)
· To leave the root directory and go back to the sherline directory:
Click on the K-icon, select Logout > End session only > OK
Type, username: sherline, password: sherline.
· On the Linux desktop, right click anywhere on the empty desktop and select Create
New>Device>Hard Disc Device.
· Under General, instead of Hard Disc Device type the words Flash Media.
· Under Device from drop down menu choose /dev/sda1 (media/flash).
· Click OK and right click again on the new icon (Flash Media) and select Properties.
· Under Permissions choose under Group and Others, Can Read & Write and check the
box in front of the words Is executable > click OK
In newer versions of BDI under Properties >General if you click on the hard disc drive
icon there is the menu with icons where the appropriate icon can be found and selected.
Note that the Flash Media device uses the same Mount and Unmount commands as a
floppy drive.
Other than calling Sherline, where are some places I can go to get help on my
specific questions on machining, cnc and using Sherline tools?
Sherline owner discussion groups can be found at http://www.yahoogroups.com. Just go
to the yahoogroups.com web site, type in the name of the group you wish to monitor or
join and select it from the list provided. You can click on “join this group” to become a
member or you can just read the archives without joining. These groups can be a very
helpful resource for anyone new to machining and a great place to go to get advice from
experienced users on specific problems. Here are some of the groups:
Sherline (3000+ members)
Sherline CNC (1000+ members)
CAD/CAM/EDM/DRO (not Sherline specific, 4000+ members)
You can always find the most up-to-date version of these instructions at
http://www.sherline.com.
What is GPL and what does it mean to me?
GPL is a license that Linux and EMC are both released under. Basically (very basically)
it states that all code released under this license can be used, modified or sold as a
prepackaged product, but it must be released under the same license after you modify it.
This helps the Linux and other open source communities grow as people contribute to it.
What does this mean to the average user? Nothing. If you decide to hack up the kernel,
however, you are required to submit those changes back to the community. More
information about GPL can be found here: http://www.gnu.org/copyleft/gpl.html
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Are these instructions updated periodically?
Yes, we are constantly trying to improve the instructions. You can find the most up-todate version of these instructions at http://www.sherline.com/CNCinstructions.htm.
Compare the version number at the very beginning of the instructions to see if it is newer
than the version you have been using. If you find an error or have questions or
suggestions about this or other documents included with your CNC system please e-mail
craig@sherline.com.
Can I mill threads without a cnc rotary table?
No problem. This program would do the job. The reason I switched to incremental was I
could use the copy and paste edit program for each revolution of the thread.
%
g90 g40 g49 g00 x1 y0 z0
x0
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g91g02 x0 y0 z-0.100 i0 j0.5 f6
g90 g00 x0.5
z0
x1 y0 z0
%
This program would cut six threads at 10 TPI.
Is there a way to convert a photo to g-code?
There are programs that will translate the dark/light scale of a photo into assumed heights
(darker is deeper) and create a 3D g-code program to reproduce the contours. One called
DeskART will import a BMP, GIF, JPEG, WMF or TIFF image and convert it into a
DXF Surface Mesh of 3D faces or write it directly into machinable G-code. See
www.deskcam.com/deskart.html. They offer a free 30-day trial version of this software.
DeskKAM also offers several other types of programs for engraving. Prices are listed at
www.deskam.com/products.htm.
What if I have a question that wasn't answered here?
If you need more information about prices, accessories or availability, customers in the
USA or Canada can call our toll free number: (800) 541-0735 M-F, 7:30-5:00 PM
(Pacific). If you have other Sherline-related questions and we can't answer them, we'll do
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our best to point you in the right direction. Outside the USA or Canada, call (760) 7275857 or fax (760) 727-7857. You may also e-mail Sherline tool related questions to
craig@sherline.com. Cnc-specific questions from system owners should be directed to
the Linux group at www.Linux.org. The best source for information on Sherline tools 24
hours a day is always our web site at www.sherline.com. Sherline tools and accessories
can be purchased factory direct 24 hours a day at www.sherlinedirect.com or you can see
our Sherline dealer list for a dealer nearest you.
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